Manju George 0:00
Hello everyone. Welcome to DocTalks. I’m Dr. Manju George, the Scientific Director of PALTOWN, the nonprofit that supports COLONTOWN. Today, we have Dr. John Strickler with us, who will talk to us about HER2 targeted therapies. But before we start, I was interested in knowing how you got to GI oncology and to running such interesting trials. Dr. Strickler, could you give us a brief look into your professional journey up to this point?

Dr. John Strickler 0:33
Yeah, so when I was going through my medical oncology training, I knew I wanted to be in academia, and I wasn’t sure which field to choose. And one of the things that spoke to me about GI oncology and colorectal cancer research is that while we’ve made tremendous progress in personalized and targeted therapies, there’s still so much more progress to make. And for me, it felt like an area that was very exciting, innovative, and an area that still needed so much more done. So for me, I saw it as a challenge and a thrill to be part of a community that up until I finished fellowship, has really only made incremental improvements in the outcomes that really matter to us, and I wanted to bring in more chemotherapy-free regimens and innovative regimens. And through my time on faculty, I’ve seen this vision come to fruition in several cases where we’ve been able to move away from chemotherapy into chemo-free regimens. So that’s been exciting for me to be part of that, and something that has really fueled my desire to continue working in this field and make breakthroughs.

Manju George 1:52
Okay, okay, nice to know. And other than taking care of patients and running clinical trials, what do you do to have fun?

Dr. John Strickler 2:02
Well, I have a family that I that I spend most of my free time with, and I enjoy going jogging when I get my own personal time, but usually when I’m doing something for fun, I’m doing it with my kids, either traveling or hiking or going to sports games with them, or whatever they’re interested in. So that’s that’s how I spend my time.

Manju George 2:26
Okay, okay, nice to know. Okay, then let’s get started.

Dr. John Strickler 2:31
Absolutely. So my topic here is HER2 as an emerging target in patients with metastatic colorectal cancer. And I wanted to start first with what inspired me to get into GI oncology and in research, and really it’s this promise of personalized medicine, this idea that knowledge of a molecular profile can potentially be used to identify patients for the right treatment at the right time. So that’s not just avoiding ineffective treatments, but also finding, based on the molecular profile, what’s going to be active and targeting that without chemotherapy, so getting the same or better results without all the side effects that we know about with conventional chemotherapy. So that’s been my fuel from day one in my area of research, and during my time, what we’ve seen is a real, substantial change in how drugs are developed. In the olden times, like 10 years ago, we had this traditional model of drug development where we would take a large group of patients and randomize them to ‘intervention A’ or ‘intervention B’, and we would squint our eyes on the Kaplan-Meier curve to see who did better. And based on that small incremental benefit, we would see FDA approvals. But that was not a biomarker oriented approach. That was more just an ‘all comers’ approach. With the personalized medicine model, we have a radical transformation in how we do research. Now we’re taking a very small group of patients and with a molecular analysis of tumor, assigning them to a precision medicine approach, and what we’re seeing is massive benefit in these highly selected patients, where it’s not even ethical for us to randomize them away to the standard of care because this intervention is so much more effective than the standard of care that no one would agree to go on the standard of care. And increasingly, thankfully, the FDA is looking at this data without control arms and approving these therapies. So this is the new era in which we live, and that’s the framework in which a lot of this work was done in HER2.

Dr. John Strickler 4:48
So going back, the end of my fellowship was in 2011 and at that time we had one actionable biomarker, and it was the KRAS mutations, but it wasn’t an actionable marker. It was inactionable. Meaning, if you saw it, you didn’t do something, you didn’t give an anti-EGFR therapies. Fast forward to 2022 we’ve got a much more interesting pie with all different kinds of slices, and this pie is growing every month as we find new targets, new things that are actionable. The encouraging part of this is that the “no biomarker” group is shrinking, and I hope it will continue to shrink in the future. The slice of the pie that I’m going to focus on today is, of course, HER2, or HER2 amplification. So with that, I will go forward with this presentation. So how do we get to HER2 as an actionable target? Well, HER2 has been known about for many, many years, and it was even studied almost 20 years ago. Trastuzumab has been around for over two decades, and the natural question is, why? What happens if we give trastuzumab to a patient with HER2 positive colorectal cancer? Well, this was done and published by a colleague of mine, Dr. Ramanathan. And interestingly, even though the response rate was quite high for the combination of FOLFIRI and trastuzumab, actually they had partial responses in five out of seven patients. The conclusion of the paper is that the low over-expression rate of HER2/neu colorectal cancer limits the usefulness of this biomarker, so there’s no point developing treatments in this area.

Dr. John Strickler 6:35
So this was 2004 and with that, the target HER2 was thought to be undruggable in colorectal cancer, because we’ll never find these patients. Well, we can thank the Italians for resurrecting HER2 as a target, but there’s a circuitous story to how we got to HER2 and it starts with EGFR. And this is a figure out of the New England Journal of Medicine, showing how EGFR works. So with my pointer here, you can see that this is EGFR, which is a so-called receptor tyrosine kinase, and we have drugs for this. We’ve got, well, let me back up: EGFR is highly expressed in colorectal cancer, and it drives some key features of all tumors; So, adhesion, angiogenesis, cell proliferation and cell survival. And we have two drugs that treat that, cetuximab and panitumumab. Now, there are some other key members of the HER EGFR family, ERBB2, otherwise known as HER2, HER4, HER3. So EGFR is a part of this family of receptor tyrosine kinases, and when EGFR is even capable of binding together with HER2 or HER3 to form what’s called heterodimers and activate downstream pathways to affect all of these properties that can lead to cell proliferation and tumor growth. So this is clearly an important target in colorectal cancer, and one in which we have several therapies in the clinic.

Dr. John Strickler 8:14
Now the first finding – as I mentioned, that emerged – and this was while I was a trainee, was so-called KRAS exon 2. And in patients with KRAS exon 2 mutations, as shown here, there is no survival benefit for anti-EGFR therapies, but in patients without mutations, you can see here that the patients getting cetuximab or anti-EGFR therapy do much better than those patients who get supportive care alone. So with that came our very first biomarker, KRAS exon 2, or KRAS codons 12 or 13. This figure depicts all of the different KRAS mutations that can occur in a colorectal cancer tumor. And we can see here that KRAS exon 2 codons 12 and 13 are by far the most common, as shown here. But there are other rare mutations that we see as well, KRAS exon 3 and 4, and NRAS exons 2, 3 and 4. These are very uncommon compared to the standard KRAS exon 2 mutations. But interestingly, they function just the same way. So patients who have a KRAS or an NRAS mutation, regardless of where/what exon it came from, are resistant to anti-EGFR therapies, whereas those patients who were wild-type, are sensitive, and that’s what this figure depicts, is that the patients who are truly benefiting from anti-EGFR therapies are those patients who have nonmutated tumors, as shown here. So already, we’re getting a lot smarter about who to give anti-EGFR therapies to. But could we be even smarter? Can we find even more mutations that could predict resistance? The next one on the list is so called BRAF or BRAF V600E. And this was a large analysis of many clinical trials looking at the impact of BRAF V600E on cetuximab and bevacizumumab or anti-EGFR therapies. And once again, it was found that patients with BRAF V600E mutations get very little benefit from anti-EGFR therapies. So now we’ve got KRAS, NRAS and BRAF V600E on our list of therapies that a list of mutations that drive resistance to anti-EGFR therapies.

Dr. John Strickler 10:37
But what else do we have? We’ve got, in addition to those mutations, there are others. There’s MET, as shown here, and something I just mentioned prior, ERBB2, otherwise known as HER2, and increasingly, there’s some work being done that has shown that these drive resistance as well to anti EGFR therapies. I wanted to go into a little bit more about why we think ERBB2 or HER2 drives resistance. This is a plot that shows in in orange, all the alterations that occurred in 2000 patients in the Guardant360 database. And you can see here from the Guardant360 database that ERBB2 amplification is quite rare, or HER2 amplification is quite rare. I then at Duke, ran a series of Guardant360s to look at what’s enriched in patients who progress on anti-EGFR therapies. And here HER2 was enriched, so we do see higher rates of HER2 amplification after progression on anti-EGFR therapies. And this is a drug double target. We have therapies for this in the clinic, albeit for other tumor types. MET amplification is also enriched in patients who progress on anti-EGFR therapies, but that target is not quite as actionable. So that’s why I personally got interested in HER2, is because I was seeing this become enriched, or seen at higher rates in patients who had progressed on anti-EGFR therapies.

Dr. John Strickler 12:17
So what do we know about HER2, its biology and its epidemiology? Well, HER2 is a so called receptor tyrosine kinase, much like EGFR. This HER1 is another word for EGFR. HER2 is in the family, right next to HER1 or EGFR, and it forms heterodimers with other receptors, whether it be EGFR or HER3 and activates this so called PI3 kinase pathway leading to cell growth, differentiation, survival and angiogenesis. So we know that HER2 amplification or HER2 positivity drives tumor growth. Additionally, what’s particularly interesting for me is that there are multiple therapies already in the clinic that very effectively target HER2 so why is it that our colorectal cancer patients have been left out? And that’s something that inspired me to start doing some work here. Now HER2: How do we recognize this and how, as a patient, would I know that my tumor would be more likely to be HER2 positive? It is typically associated with left-sided primaries. So when I say left sided, that’s rectal sigmoid and this area of the colon here, up to the descending colon, that’s classically where we see these HER2 positive cancers originate. It’s not mutually exclusive with RAS or BRAF mutations, but it tends to occur at higher rates in patients who have RAS wild-type and BRAF wild- type or nonmutated disease. Interestingly, it’s not associated with worse prognosis. So we think about HER2 as a bad actor in breast cancer, but in colorectal cancer, not so much. And there’s a lot of questions about whether this drives resistance to anti-EGFR therapies. So in terms of how often we see HER2 amplification, it’s usually, in most large data sets, around 3% of patients. We’ll see it in about one in 40, one in 30 patients. And interestingly, when we know where to look, it’s much more common. So in KRAS wild-type, or RAS and BRAF wild-type, we see much higher rates of HER2 amplification. So the real, the most common scenario, would be someone with a left-sided RAS and BRAF wild type, microsatellite, stable, tumor. That would be where we see rates upwards of 10 to 12%.

Dr. John Strickler 15:06
The next question is, does HER2 drive resistance to anti-EGFR therapies? And this is really the million dollar question here, and something that we still have very active debates about. So this is work that was done in Italy a number of years ago, a little over a decade ago, where they took a large number of patients and biopsied those tumors and then grew those tumors in mice. And all of these tumors were thought to be KRAS wild-type, and they looked at what drove sensitivity or resistance to cetuximab, the anti-EGFR therapy in their mice. And each bar here represents an individual mouse, and the HER2 positive tumors have a star at the top, and you’ll notice very little disease control in those tumors that were HER2 positive so HER2 negatives were all over here, and they did the best with cetuximab. So that was the first clue here, that HER2 drives resistance to cetuximab. And then we have some retrospective data. So this is a large data set out of Italy where they took 100 patients that were HER2 positive and compared outcomes with anti-EGFR therapies, compared to those who are HER2 negative. Pretty large data set, and they found a few things. First, that HER2 positive disease is associated more with lung metastases than liver metastases, and it was more likely to be left-sided, as I mentioned. Here, this retrospective analysis found that patients with HER2 positive disease did worse with anti-EGFR therapies than patients with HER2 negative disease. So this is our first clue that HER2 drives resistance to things like cetuximab and panitumumab. The group at MD Anderson also looked at their data to compare outcomes for anti-EGFR therapies and patients with HER2 positive disease, and found, once again, the yellow represents HER2 negative and the blue represents HER2 positive, and those patients treated with anti-EGFR therapies did worse if they were HER2 positive. They then went back to look at the prognostic impact of HER2 positivity, and found that there was no prognostic impact. So they did all the same on first-line chemo, but when it came to giving an anti-EGFR therapy, they did worse with HER2 positive disease, really isolating the effect of HER2 amplification on resistance.

Dr. John Strickler 17:48
So now let’s go into some key studies that showed how well these anti-HER2 therapies, which are already approved for breast cancer and in some cases, gastric cancer, how they do in colorectal cancer. Well, first starting with the mouse data. The key point here is that there is some activity for anti-HER2 therapies given alone. But at least in the mouse work, it suggested, if you’re going to give an anti-HER2 regimen, better to give two drugs than one, and that’s the key lesson here, based on our preclinical data. So this is what we expect based on this in the clinic, is that two drugs would work better than one. And that gets us to our very first study that entered the clinic. This is the so called HERACLES-A trial that was published in 2016. This was a wonderfully designed and executed study. It took patients who had progressed on at least two different lines of therapy for metastatic colorectal cancer. They all had KRAS wild-type disease. They had all progressed on anti-EGFR antibodies and 27 patients were treated with combination of lapatinib, which is a pill, and trastuzumab. Now this is an approved regimen for breast cancer. The primary endpoint was response rate, and here in this study, the initial data showed a response rate of 30% so that’s a very good response rate where the current standard of care has much lower response rates. 84% of patients had tumor shrinkage. And interestingly, they found that seven of eight patients who had a response had the highest level of HER2 expression, this so-called IHC 3+. This is a marker of expression, and that’s the maximum level. So that’s what’s shown here in red, that these patients with the highest level of expression clearly did the best.

Manju George 19:46
Dr. Strickler, can I interrupt for a bit? Could you please tell us about trastuzumab versus lapatinib? How they act and how combining them a little bit about the rationale?

Dr. John Strickler 20:00
So thank you. These are very different drugs. Lapatinib, as shown here, is a pill, and it’s a so-called tyrosine kinase inhibitor. So it binds HER2, but it also binds other things, things like EGFR, so it does have a bit more toxicity, meaning rash and diarrhea and some symptoms that limit our ability to give a full dose. Trastuzumab, on the other hand, is an antibody, and this one is approved for breast cancer and gastric cancer. This one is a is a bit better tolerated. It doesn’t have the same diarrhea or rash side effects, but it does have, in rare cases, some cardiac toxicity, so it can make the heart function go down in some patients, pretty rare, but it can occur, so this one is better tolerated, but it does affect the heart in rare cases, and then this one is a bit rougher, and in this model, had a bit more activity as single agent than trastuzumab. But clearly, if you’re going to give this, better to give it together, because in these mice models, these tumors did not grow on the combination, but you can see they eventually grew on just a single agent. Does that answer your question?

Manju George 21:22
Yes. Yes, thank you.

Dr. John Strickler 21:26
So you know this was really outstanding. Data out of the HERACLES trial, progression-free survival was around four months, and once again, it was those patients with the highest level of expression, as shown in red, that had the most durable responses. And so while most of us are getting what’s called ‘next gen sequencing’ done, or NGS testing, whether it be Caris, Foundation,Tempus, and getting that type of testing done to find the HER2 positivity, there is something to be said for this old fashioned HER2 immunohistochemistry, which has been done for decades, which is able to capture the expression of the protein and is a really good way to see how well this therapy might work, even before you take it. The other marker that they looked at in this HERACLES study is this gene copy number. So, ‘expression’ is how much protein is on the surface of the cell. ‘Gene copy number’ refers to how many copies of the gene are in the nucleus. So higher means more amplified, and higher means that the tumor is more addicted to HER2. And as you would expect, the higher the copy number, the more addicted that tumor cell was to HER2, and the better the patient did if you attacked that HER2 right? So that tumor is addicted to HER2. And if you give an anti-HER2 regimen, you can really stop the growth of the tumor, and in some cases, very durably, so the long term outcomes of the HERACLES study looked promising. Response rate was 28%; Progression-free survival was an impressive 4.7 months, which is better than our standard of care at the time. And some patients had responses ongoing for over five, or one patient had a response ongoing for in excess of five years. So that’s pretty impressive to see.

Dr. John Strickler 23:24
I won’t spend a lot of time on this because it’s very difficult to explain this, but the key thing to know is that just as KRAS can drive resistance to anti-EGFR therapies, it can also drive resistance to anti-HER2 therapies. So when there’s a KRAS mutation, or a BRAF mutation together with HER2 positivity, HER2 amplification, that does drive resistance to our anti-HER2 therapies, and that’s what has been shown in the HERACLES study. I won’t spend a lot of time on this figure because it is a bit complicated, but the key message here is that KRAS drives resistance both to cetuximab and panitumumab, and in cases of HER2 amplified disease, anti-HER2 therapies, one of the things that I’ve mentioned before is that copy number refers to the number of copies of the gene, and sometimes we can identify the copy number in blood with a circulating tumor DNA assay. So this group from the HERACLES trial looked at copy number in blood, and they found that those patients in red with the highest copy number in blood also did the best. These are the tumors that are most addicted to HER2, and will be most effectively treated with an anti-HER2 regimen. So that was our first foray into treating HER2 positive disease.

Dr. John Strickler 24:50
The next was this so-called ‘MyPathway’ trial. And MyPathway was started by Genentech as a way to explore a number of different therapies in a so-called ‘basket’ or ‘umbrella’ design. Here they looked at, in this HER2 arm, the combination of trastuzumab and pertuzumab across a broad range of solid tumors, and colorectal cancer was the largest group, as shown here, with 84 patients. That went on over several years. And as I said, all patients were treated with trastuzumab and pertuzumab had progressed on at least two lines of therapy and they allowed patients on with any type of local testing was permitted – so patients could go on if they had a Foundation medicine, or a Caris, or an IHC. They did not apply one test as criteria, which I think was very, very much patient-oriented, because we all know that everybody’s getting different kinds of tests, and we want to be as accessible as possible with these kinds of trials. And the primary endpoint in this study was response rate. The response rate overall was 32%, very similar to what I just showed you with HERACLES. But one of the things you’ll notice is that in those patients who had a KRAS mutation, very few responses. So just one response, as shown here with the ‘K’. Each bar here represents an individual patient. Almost all the responders had no KRAS mutation, or so called wild-type, and the response rate in their initial data was 40% which is, overall, very promising. The progression-free survival overall was okay at 2.9 months. But once again, when you look at those patients who did not have a KRAS mutation, they did much better, 5.3 months progression-free survival. Once again, really impressing upon us the importance of those KRAS mutations in predicting resistance to these kinds of therapeutic strategies. The good news here is that KRAS mutations are fairly rare together with HER2 amplification. Most of the time, KRAS mutations are not there with HER2 amplification, but occasionally they will be.

Dr. John Strickler 27:19
Moving on now to this next slide looking at all the potential markers: As I mentioned, KRAS status appears to matter. Those patients who are nonmutated or have KRAS wild-type tumors have a response rate that’s better than those who have mutations, progression-free survival also better. PIK3CA status may also matter. So PIK3CA mutations appear to drive resistance to these therapies as well. So that’s something to be aware of. The good news here is, it does not matter if you’ve had a prior anti-EGFR therapy or not. The response rate, the progression-free survival is very similar. So KRAS and PIK3CA appear to be important. There have been several other studies that have looked at trastuzumab and pertuzumab for HER2 positive metastatic colorectal cancer. I’ve put all of those trials here on this table. All of them are zeroing in on very similar data. Response rates of right around 30% or so. Progression-free survival, I would trust this number the most. The 4.0 ones is probably the most accurate number. I will point out that ASCO TAPUR posted a much lower response rate of 14% but that’s because they probably included a large number of patients who had KRAS mutations.

Dr. John Strickler 28:44
So let’s go back to my clinic. As I said, I’ve had an interest for a long time in understanding drivers of resistance to anti- EGFR therapies, and one of the markers that came up is MET amplification but the other one is pertinent to this talk today, and that’s HER2 amplification. It became clear that we were identifying these patients, but we didn’t have FDA approved therapies, and we didn’t have any options in the clinic, and there were starting to be these hints from the Italians and others that this is a druggable target. So all of my research is inspired by my patients. My patients teach me, and I would say that the most impactful trials come from those people who know patients the best and know what patients are dealing with, both in terms of side effects, tolerability, activity, resistance. And this is an actual patient from my clinic who inspired the MOUNTAINEER trial. This is a 58 year old guy, and he permitted me to tell of his story. He presented several years back with bright red blood, per rectum, fatigue, abdominal pain and anemia. This is a familiar story to COLONTOWN, PALTOWN, and the rectal biopsy confirmed adenocarcinoma. At the time that he was diagnosed, there was no such thing as HER2 testing. We had a hot spot panel that only looked for KRAS, NRAS and BRAF, and these were nonmutated, otherwise known as wild-type. He got standard therapy, which is FOLFOX and bevacizumab, did fine for a while, but then, unfortunately, progressed. Then he got second-line, FOLFIRI and the anti-EGFR therapy panitumumab, and then went on a third-line, regorafanib-based trial. And when I met him, he was quite sick. He was coming for trials. And I obtained a Guardant360 liquid biopsy to look at what was going on with his tumor, and understand if he might be eligible for one of our studies.

Dr. John Strickler 30:45
This is what his blood profiling revealed. He had a very classic pattern of TP53 mutation, a high allele frequency, and APC mutation. And then further down, this is HER2, ERBB2, and this ‘+++’ is the highest score possible for somebody with this blood test. So he was off the charts for HER2 positivity. And this was a surprise to me, because I didn’t know he had it based on the tissue test. So we went back to the tissue to understand whether this was just something that was in the blood only. And we found that the tumor was highly amplified for HER2, and this is by the so called, FISH test, where we count the number of copies of HER2 and compare it to the center of the chromosome. And this ratio, anything over two is amplified, and his was 10.59 – so highly amplified. And I said, “Look, there’s nothing FDA approved for you, but I’ve heard some data from the Italians that this combination of lapatinib and trastuzumab might be active”. So I applied for access, and he was fortunate, because they allowed him access to off label lapatinib and trastuzumab. This was the baseline scan. These green lines represent tumor lesions in his liver. He was quite sick at the time. He had a lot of pain in the right upper quadrant from from these spots, and within days of starting this new regimen, he felt much better. So after six cycles of lapatanib and trastuzumab, or about four months, you can see here the tumors were almost entirely gone. He felt dramatically better. But a few things first, he did struggle with the side effects of lapatanib, which include rash and diarrhea, and I was not able to give him the full dose of lapatanib because of all those side effects. And so that was a frustration. And then the second frustration is that, why don’t we have treatments for these people? This target is just as actionable for a patient with colorectal cancer as it is for a patient with breast cancer, and I wanted to bring some treatments into the clinic, so I reached out to a company in Seattle called Cascadian, because they had a new oral therapy that was much more potent against HER2 than the patented, with fewer side effects. And they said, that’s a really interesting idea, John, let’s try this in colorectal cancer.

Dr. John Strickler 33:22
The first thing we did was we looked at how well it worked in these lab mice. Well, each curve here represents an individual mouse model. And what I would point out to you here is that in the group, the mice that did the best are characterized here in blue. So right here, and these are the mice that received the tucatinib + trastuzumab combo, much better result than either tucatinib alone or trastuzumab alone in all the models. So we felt like there was a strong rationale. It was already working in breast cancer, and there was something here. So that gets us to MOUNTAINEER, which was presented just about a month ago in Barcelona, as well World GI. This was a global open label, phase II trial that was initially started as an investigator-initiated trial in the United States. I initially wrote the protocol, and we opened it. Our first sites included Mayo Clinic and Dana Farber, Memorial Sloan Kettering, Emory, and a few other sites. And this was initially written as a study to look at the combination of tucatinib and trastuzumab, no chemotherapy, and we allowed patients on — you know, I’d like to say this is a study by the patients, for the patients, right? We aren’t going to delay enrollment, waiting for some central lab to confirm HER2 positivity. If the patient had a test from any hospital or any vendor that said they were HER2 positive they were allowed on and that’s very different from many sponsored trials that we’re accustomed to, or you have to wait a month to tell you what you already know. All patients had RAS wild-type disease, because we felt like that was really important as a predictor of sensitivity, and patients had either progressed or developed intolerance to FOLFOX/ FOLIRI and an anti-VEGF. We did not require progression on an anti-EGFR antibody because the feeling of the investigators is that HER2 drives resistance to anti-EGFR therapy so why would we force a patient to take it before going on?

Dr. John Strickler 35:44
We presented this initial, Cohort A result in Barcelona, and at ESMO in 2019, and then, based on that result, the study was transferred to Seattle Genetics, who acquired Cascadian, and they expanded the study for potential FDA registration. So it became a randomized study where patients were randomized either to tucatinib and trastuzumab combination, or tucatinib alone. Now I had concerns about tucatinib alone because I felt like the data was pretty strong, that we needed to give a combination, but in order for it to receive an FDA approval, the FDA wanted to get some sense of the clinical activity of tucatinib by itself. And in order to make it more palatable to patients being randomized, we allowed patients to cross over from tucatinib alone to the combination if there was not a response by 12 weeks of treatment. A primary endpoint was response rate, as I mentioned, HER2 is associated with left sided disease, and that’s exactly what we found. Over 80% of patients had left-sided disease. And interestingly, we did find that HER2 positive disease was strongly associated with lung metastases in this model, and it may be that patients with lung metastases are much more likely to have HER2 positive disease. This was a heavily pretreated patient population, so about 80% of patients had received two or more prior lines, and some of the prior treatment history is shown here, the response rate, and this is the key endpoint of the study, the confirmed objective response rate was 38%. Now what do we mean when we say confirmed objective response rate? What this means is that there was at least a 30% reduction in the target lesions, and that that response was sustained over two scans, so there were many patients who benefited. It was not just 38% – many patients benefited, but this is a confirmed reduction greater than 30% over two scans. What we also found particularly impressive was that those patients who did experience a response that that response duration was quite long. It exceeded 12 months, which is better than what we’ve seen in other anti-HER2 studies. So we are particularly encouraged by that result as well.

Dr. John Strickler 38:12
So one measure is, of course, the technical response rate by the so called RECIST criteria, but we can see that there are many other patients who benefited. And in fact, two thirds of all patients had a reduction in their measurable tumor lesions while on study. So we actually saw 65% of patients experienced some shrinkage in their disease burden while on treatment. And there were some patients, as shown here in the light blue, had a complete response to treatment. So all very promising data that we presented about a month ago, we also found that across a number of subgroups analyzed that there was similar response rates. So response rate didn’t matter by age, by performance, status by geographic region of the world, there is a hint here that potentially we can see higher response rates in patients with left-sided primaries compared to right-sided but this is pretty preliminary data, and we just didn’t have enough patient numbers to make firm conclusions about that. Progression-free survival here was also impressive at 8.2 months, with a median overall survival exceeding two years. And I will point out that that median progression-free survival in excess of eight months is comparable to what you would expect out of a front-line chemotherapy for patients with newly diagnosed metastatic colorectal cancer. So remembering that the current standard of care in some cases is things like TAS-102, or regorafenib where we expect progression-free survival closer to two months. This is all very promising data. We also looked at the clinical activity of tucatinib monotherapy, and not surprised, the response rate here was much lower. Only one patient responded, but most of these patients crossed over after 12 weeks. So based on this, I think we can say that we observed much more durable and long lasting clinical activity out of the combination of tucatinib and trastuzumab. Interestingly, though, tucatinib monotherapy still works. We saw a disease control rate of 80%. One of the things that is encouraging to me as a clinical provider, is that this combination of tucatinib and trastuzumab appeared to be well tolerated.

Dr. John Strickler 40:44
Only five patients discontinued treatment due to an adverse event, and that includes one patient who came off due to COVID-19 pneumonia. There were no treatment-related deaths. Once again, that’s something that’s so important to us in the clinic, that there were no deaths that thankfully occurred due to the study regimen.

Manju George 41:06
Dr. Strickler, I have a question. So how does tucatinib compare with lapatinib in terms of how it acts and also the side effects? Does it also have the activity against EGFR?

Dr. John Strickler 41:22
I’m so glad you asked that. So I actually skipped over that point, but I think it’s a really important point on this slide here. This table compares what’s called, “the IC-50s”, how potent these three drugs are. Tucatinib, lapatinib and neratinib, against two targets. One is HER2 and the other is EGFR. The lower the IC-50, the more potent it is against the target. You’ll see that tucatinib has a very low IC-50, at 6.9. Lapatinib, 109, so lapatinib has less activity against HER2 than tucatinib, then looking over here at EGFR, now, most of the side effects people get from these pills happens not because of the HER2, it’s the EGFR. So you actually want to see low potency against EGFR, and here tucatinib has an IC-50 of that’s very high, 449. Lapatinib, 48. So it’s lapatinib is 10 times more potent against EGFR, which probably explains why we see so much more rash and diarrhea with lapatinib as compared to tucatinib. There’s another drug that’s used in the clinic in breast cancer, neratinib, and this one is extremely potent against EGFR. So this was another reason why I was particularly interested in tucatinib, because it does attack HER2 very effectively, but has limited effect against EGFR, which is what we want to minimize the side effects.

Manju George 43:06
Okay, thank you very much.

Dr. John Strickler 43:09
Yeah, that’s a great question. So this table here shows the most common adverse events or side effects for patients who got the tucatinib + trastuzumab combination. Blue represents grade one, or pretty low grade, or mild. Two represents moderate toxicity. Grade three is purple, which means more severe side effects, and we see very little purple, and the most common tucatinib related adverse events here, and this is important to note, diarrhea, fatigue, nausea and there is some rash even with tucatinib, even though it has much less effect against EGFR. Now, as I mentioned, diarrhea is the most common side effect to expect with tucatinib, but in most cases, that was mild, 50% were mild. We saw more moderate range into 10.5%. Only 3.5% of patients had grade three or more severe. Interestingly, there were no treatment discontinuations due to diarrhea, so we noticed it, but it’s not appearing to impact our ability to treat with it, and only 2.3% of patients had a dose reduction of tucatinib due to diarrhea. So while it’s the most common side effect, it appears to be manageable in most cases. We did see a couple rare cases of liver toxicity, otherwise known as hepatotoxicity, we saw 3.5% of patients with increased ALT, 2.3% with increased AST. And what happened in those rare cases is that we would stop the drug and it would resolve over about three to five weeks. The patients usually didn’t even notice, but it was something that we just saw in the labs. And this is another important side effect. I mentioned that trastuzumab can cause heart dysfunction, and this did occur in 3.5% percent of patients. So this is something not related to tucatinib, this is related to trastuzumab.

Manju George 45:17
I was wondering with the hepatotoxicity. How comparable is it with, say, just oxaliplatin mediated increase in AST and ALT?

Dr. John Strickler 45:30
Well, I would say that most many patients were seeing very small increases in the AST and ALT. I would say it’s, in my own personal experience more than you would expect with, say, oxaliplatin or irrinotecan, the good news here is that it rarely results in a level of liver toxicity that would lead to modification or discontinuation. So it is something to be mindful of, that there are a few folks, unfortunately, who did run into this problem, and it’s something that needs monitoring if you’re on this treatment, but it’s one of these things where you would not notice it or feel anything as a patient.

Manju George 46:17
Okay. And then here, the slide says, antidiarrheal prophylaxis was not mandated. Does that mean to say that it was so mild that patients were okay without treating the diarrhea? Is that what it means?

Dr. John Strickler 46:30
What it means is that we did not say that everybody needs to take Imodium before they start. We would only bring in the Imodium or lomotil if the patient developed grade one intolerable, or grade two diarrhea, or worse. So we would only bring in the antidiarrheals if the patient was struggling with that symptom.

Manju George 46:54
So I think that basically, that language in the trial that you did not mandate antidiarrheals.

Dr. John Strickler 47:01
That’s right, that’s right. So this is where we stand in terms of the treatment landscape of dual anti-HER2 therapies. We’ve got lapatinib + trastuzumab, response rate of 28%, progression-free survival is here… MyPathway is pertuzumab and trastuzumab, 31% response rate, 5.3 months, progression-free survival. And now we’ve got MOUNTAINEER data tucatinib + trastuzumab: larger group of patients, 84 patients, response rate of 38% progression-free survival, 8.2 months. So the first two are in our national guidelines, NCCN guidelines, and are accessible. The third – tucatinib and trastuzumab is not yet in our guidelines. I hope it will be soon.

Dr. John Strickler 47:48
But we’re not done. We have other anti-HER2 therapies in the clinic. This is trastuzumab deruxtecan, this is a very different kind of molecule. This is basically Herceptin attached to a very potent chemotherapy that’s kind of related to irinotecan. It’s called deruxtecan. DESTINY-CRC-01 showed the first data for this drug in HER2 positive colorectal cancer. I will point out that they also looked at the activity for this drug in patients with lower expressing tumors. So this is Cohort B and Cohort C, and I’ll point out that, unfortunately, there were no responses in their initial data with pretty short progression-free survival. Most of the activity we saw came out of Cohort A, which is these, HER2 positive tumors, IHC3+ or 2+FISH amplified. No patients were allowed on with it HER2 positivity by next gen sequencing. So this did require a central assay. And the good news here is this is a very active therapy. Confirmed response rate in the initial data set was 45%, disease control rate also very high at 83%. The median duration of response was at seven months. So that’s a meaningful benefit, progression-free survival at 6.9 months. So the initial data out of Cohort A looked very promising. Here’s the key thing to know about this drug: It is an antibody drug conjugate. It is attached to chemotherapy so you can get more chemotherapy related side effects, things like nausea, decreased appetite, platelet counts, things of that nature. But there’s also one side effect to be aware of, and that is interstitial lung disease or pneumonitis. 6% of patients did experience pneumonitis or lung injury from this drug, and in two cases out of 78 that lung toxicity was fatal. So for those patients who do take trastuzumab deruxtecan it’s very important to be alert to that potential risk. It’s rare, but that is a potential risk that typically can come on sometime between month two and three. I will point out that in this study, DESTINY-CRC-01 trial, most of the benefit was captured by patients with the highest level of expression. So IHC3+ – high, high expression, 57% response rate, much lower response rate in 2+. I don’t have this data yet for MOUNTAINEER, I hope to show it soon as well, so we can put those side by side. The other really exciting, important thing, there were many patients who went on DESTINY-CRC-01 who had already had trastuzumab, or other anti-HER2 therapy before they went on. It did not appear to impact response rate. Response rate was nearly identical whether a patient had had prior anti-HER2 therapy or not, which suggests that you could potentially give this person an anti-HER2 regimen, like what we just showed you, and then go on to trastuzumab and then go on deruxtecan if that therapy stops working or is intolerable. So that’s an important finding out of DESTINY-CRC-01.

Dr. John Strickler 51:10
There’s been some interesting work looking at biomarkers. It does seem like there are a fair number of responders and patients who have KRAS or NRAS mutations. So this might, I say, ~might~ be an option in patients who have HER2 positive disease and a KRAS, NRAS or PIK3CA mutation, but the data is still early, so I would stay tuned to that. And then here is our national guidelines as of now. So, for patients with colorectal cancer who’ve had prior first-line chemotherapy, we’ve got trastuzumab deruxtecan, or trastuzumab pertuzumab or trastuzumab lapatinib. All of these are in our national guidelines, and I hope that for those patients of HER2 positive disease, they will get access to these things. So none of these are FDA approved yet. There are several other drugs in the clinic to be aware of. ZW-25 is kind of like a trastuzumab pertuzumab, all-in-one molecule, and it appears to have some activity. And then there are a number of other therapies in the clinic. Though, response rate is variable, and I’m not sure how many of these are active trials at the moment.

Dr. John Strickler 52:25
Finally, I want to wrap up with a plug for clinical research and get people excited about what’s next. This is SWOG-1613, which recently closed. So we hope to see this data soon, and this is going to be the definitive question on whether to give patients with HER2 positive disease an anti-EGFR therapy. So patients are randomized to standard treatment that’s cetuximab and irinotecan versus trastuzumab and pertuzumab, and for those unfortunate people who are randomized to this group, they are allowed to cross over at the time of progression. The primary endpoint is progression-free survival. We’ve got DESTINY- CRC-02, which is also active, but not recruiting. And as I mentioned, we had some problems with treatment related deaths on DESTINY-CRC-01 so this is looking at a lower dose of trastuzumab deruxtecan. It’s randomizing patients to the 6.4 mg/kg dose or the lower 5.4 mg/kg dose to see which group does better. And the primary endpoint is response rate. And they did allow some patients with RAS mutations on this study so that will also help us answer that very important question of whether those patients with RAS mutations might do better with this regimen.

Dr. John Strickler 53:41
And then finally, a lot of folks want to know why they can’t just start anti-HER2 therapies right at the beginning. And that’s what MOUNTAINEER-03 is all about. And that will take all patients with newly diagnosed metastatic disease and randomize them to FOLFOX tucatinib and trastuzumab, or standard therapy with the primary endpoint being progression-free survival. So look out for that study as well. And then this is my next study coming up. This is for those patients who would have inherent, intrinsic resistance to tucatinib and trastuzumab, those patients with RAS mutations, and here we put a cytotoxic together with tucatinib and trastuzumab. So TAS-102, and this will be opening at several sites in the United States. Once again, this is for patients who have both a RAS mutation or PIK3CA mutation and HER2 positive disease. So it’s a way to make their disease more responsive to tucatinib and trastuzumab with the addition of a cytotoxic. So in summary, HER2 amplification or over expression is an actionable target. I hope everybody is excited about that after this talk. We’ve got a number of anti-HER2 therapies in the clinic. But we know who does best, it’s patients with the highest levels of expression, IHC 3+, high gene copy number and the absence of KRAS, NRAS, PIK3CA and BRAF mutations.

Dr. John Strickler 55:15
I think that we’ve seen a number of therapies that have already shown efficacy. And the key question for the physician and the patient is going to be which one to give now we’ve got all these options. Now we’re going to have to take into consideration the clinical characteristics, the efficacy, what’s going on with the tumor mutations, to give the best treatment possible, and also encourage trial enrollment. So how do I treat HER2 positive metastatic colorectal cancer now based on all this data? Off trial, front line, I would still give the standard chemotherapy as shown here, which could be either FOLFOX, FOLIRI or FOLFOXIRI, depending on the patient. And then I would only treat for four months total. On first-line, stop after four months, and then move right right next into second-line. In the right patient, I think tucatinib and trastuzumab is a very active regimen. It can provide durable disease control in many cases, with, in some cases, very few side effects, or at least manageable side effects. So I like this one next. I like to keep trastuzumab and deruxtecan around as my rescue treatment if tucatinib and trastuzumab is not effective or not tolerated. So it’s nice to have that as a backup plan. And then where it gets really messy here is out here in the fourth-line. So we’ve got many other anti HER2 therapies there, but we still have chemotherapy as backup. And then there are some other treatments that are FDA approved as well. Once we get out of this group, then I would strongly encourage trials as well. So with that, I will wrap up. Thank you for having me and allowing me to give this talk. This is a picture from the edge of my campus, right here at Duke, where we have the beautiful Duke Chapel and a wonderful campus. Thank you.

Manju George 57:16
Thank you very much. That was an excellent talk. We have some questions in the chat. We can see if we can go through it quickly. I think one common question that patients have is about amplification versus mutation. So for all these studies, it looks like amplification or the level of expression is more important, right? And that’s the first part the second part, the question they asked is, does the IHC or HER2 amplification status change over time, and does it make sense to recheck?

Dr. John Strickler 57:48
Let’s start with the first question. There’s a lot of terms thrown around, and they are quite confusing. Mutation is currently not thought to be actionable, so if you see a mutation, we don’t have any data to suggest any of these treatments are active for patients with HER2 mutated or ERBB2 mutated tumors, that’s not to say that won’t be the case in the future, but our current data suggests that mutations are unfortunately excluded from this data, so limited benefit HER2 amplification, or ERBB2 amplification, is shown on these next generation sequencing reports. That’s your Foundation medicines, your Caris, your Tempuses and that’s generally a good marker of sensitivity to these anti-HER2 regimens. But the best marker of sensitivity is HER2 expression. That’s actually looking at how much HER2 protein is on the cell that comes through a test called immunohistochemistry. And there you would want to see 3+ expression as the best marker of benefit. There is a also another marker that you’ll hear mentioned, which is ‘amplification by FISH (Fluorescent In-Situ Hybridization)’, and that just counts the number of genes in the chromosome. And the higher, the better. But you want to see a HER2 to a centromere 17 ratio greater than two, but hopefully greater than four or six. And the best response is helping in those people with eight or more, and that’s a ratio of HER2 to centromere 17.

Manju George 59:34
Okay. Thank you for that. If a person develops ERBB2 amplification after anti-EGFR treatment, is there a trial for them?

Dr. John Strickler 59:44
That’s a wonderful question. I didn’t answer the other question about rebiopsy, so I’ll come back to that. But it is possible to acquire HER2 amplification after exposure to anti-EGFR therapy. But based on what I know, therapies we have right now are for truly HER2 addicted tumors. And you would want to ensure that it’s not just a low grade HER2 amplification picked up on a blood assay. You would want to confirm in the tumor tissue that HER2 truly is driving that tumor, because those are the patients that benefit the most. So you could treat a low grade HER2 amplification with some of these therapies, but I think you’ll see the best results if you do a tissue biopsy and you show that it’s highly HER2 positive. So, I think that’s still an area of active research. In terms of, do I rebiopsy? I would say, whenever a patient progresses on an anti-HER2 regimen, I would like to know why the patient progressed. And I think biopsy, if it’s safe and feasible, is a great idea, but the alternative is to do a liquid biopsy, a blood based assay, and that will sometimes tell us everything we need to know. So we don’t always have to suffer in order to get the answer. Sometimes we can just draw two tubes of blood and get the answer much quicker and much less painfully.

Manju George 1:01:18
Okay, so if I heard it right, what you’re saying is that there is a difference between having a tumor which already has HER2 amplification, versus a tumor that acquires HER2 amplification following other therapy, right? Okay. The next question for DESTINY-CRC-01, did it make a difference for patients about the amount of time between earlier HER2 treatment?

Dr. John Strickler 1:01:47
Can you ask that question again?

Manju George 1:01:52
People with prior HER2 therapy. Did it matter?

Dr. John Strickler 1:01:58
I actually don’t know that. I don’t know the answer to that question.

Manju George 1:02:02
Okay, yeah, yeah. And then I had this question, the interstitial lung disease that you see in the deruxtecan studies, is it dose dependent? Is that why they’re thinking that they’ll start with a lower dose in DESTINY-03?

Dr. John Strickler 1:02:17
Yeah, I think there is a concern that it might be dose related. I will point out that the FDA approved dose level for breast cancer is 5.4 mg/kg. The DESTINY-CRC-01 trial used a higher dose at 6.4 and I think all of us are concerned that maybe the dose chosen is not optimized. So that’s what drove DESTINY-CRC-02 to actually randomize patients to 6.4 mg/kg or 5.4 to get a better idea of what maximizes both the activity and also the tolerability.

Manju George 1:02:53
Thank you so much. We are five minutes past two o’clock, and thank you very much for your time. This is very helpful.

Dr. John Strickler 1:02:59
Yeah, my pleasure. Thank you.