CTDNA in Colorectal Cancer

Dr. Rachna Shroff, chair-elect of the 2023 ASCO GI Cancers Symposium, and guest host Dr. Shaalan Beg discuss new research presented at GI23, including new data from SWOG 1815 in biliary tract cancers, advances in biomarker studies in mCRC such as the PARADIGM trial, and promising updates in ctDNA technology. She also highlights the exciting potential of AI in oncology.

TRANSCRIPT

Dr. Shaalan Beg: Hello, and welcome to the ASCO Daily News Podcast. I'm Dr. Shaalan Beg, your guest host of the podcast today. I'm an adjunct associate professor at UT Southwestern's Simmons Comprehensive Cancer Center and vice president of Oncology at Science 37. Today we'll be discussing key abstracts and other highlights from the 2023 ASCO Gastrointestinal Cancer Symposium, which celebrated 20 years of transformative care in GI cancers.

I'm delighted to welcome Dr. Rachna Shroff, the chair-elect of this milestone meeting. Dr. Shroff is the interim division chief of Hematology Oncology at the University of Arizona Cancer Center. She also serves as the associate dean for Clinical and Translational Research and is the chief of GI Medical Oncology.

Our full disclosures are available in the transcript of this episode, and disclosures related to all episodes of the podcast are available on our transcripts at ASCO.org/podcasts.

Dr. Shroff, it's great to have you back on the ASCO Daily News podcast.

Dr. Rachna Shroff: Thank you so much for having me. I'm so excited to be here.

Dr. Shaalan Beg: The ASCO GI Cancers Symposium has been heralded as one of the biggest conferences in the GI cancer space and has occupied this space for the past two decades. Some would say that this year's conference was probably the best GI Cancers Symposium to date. Can you comment on the 20th anniversary milestone and the impact of the symposium on GI cancers?

Dr. Rachna Shroff: Absolutely, and that's so great to hear that that's the feedback that you've heard. I have to say GI ASCO is absolutely my favorite meeting of the year, so that is my full disclosure. But I think that this was a tremendous meeting, and I think it was so beautiful that it was also coinciding with the 20th anniversary. It meant so much to us to have Dr. Margaret Tempero open the meeting because she really was the impetus for creating a GI cancer-focused meeting that really brought together multidisciplinary expertise. And so to us, that is what this 20th anniversary represented—20 years of multiple different specialties coming together to discuss how to improve cancer care for patients with gastrointestinal malignancies.

And it has been a transformative meeting to see the impact of research presented at this meeting and how it has been implemented over the course of 20 years. And I completely agree that this year in and of itself had some incredible pivotal data that there is no doubt will be practice-changing, and that is absolutely the purpose. I also think that the beauty of this meeting is the networking opportunities for all of us to come out of our individual silos, come together, and discuss cross-cutting care across the spectrum of GI malignancies. And I think that this meeting really did that quite well.

Dr. Shaalan Beg: There were many practice-changing studies that made headlines this year, and for me, one of the most anticipated studies was a trial that you led for cholangiocarcinoma and much-anticipated results. The study finished enrollment at a record pace. Can you share your key findings of cholangiocarcinoma? And I'd really like to hear your perspective on cholangiocarcinoma studies.

Dr. Rachna Shroff: Yes, it was actually a really big year in the hepatobiliary space, and I was proud to present SWOG 1815, LBA 490, which was the pivotal randomized phase 3 trial looking at gemcitabine, cisplatin, and nab-paclitaxel versus gemcitabine and cisplatin. This was a study that was opened across the entire NCTN and based on a single-arm phase 2 trial that had shown some promising early efficacy of the triplet chemotherapy regimen. As you mentioned, this study accrued 441 patients in two years. And it's really a testament to the fact that the cooperative group mechanism can and should be asking important questions in large, randomized studies and that it is even possible to do in what are historically thought of as, quote-unquote, "rare tumors."

The study was a randomization of two to one to the triplet chemotherapy versus the standard of care for newly diagnosed biliary tract cancer patients. And the primary endpoint was median overall survival. And while the median OS of the triplet regimen was numerically improved at 14 months compared to 12.7 months, this did not meet statistical significance. Other efficacy endpoints, including median progression-free survival and overall response rate, were also numerically improved but not statistically significant, with an overall response rate of 31% with the triplet regimen versus 22%. There were some prespecified stratification factors, including disease site and disease stage, and there may be some interesting signals that bear out of that in terms of perhaps gallbladder cancer and locally advanced patients may be benefiting from the triplet regimen a little bit more, but these are small numbers, and we would really need to explore that in a more rigorous prospective manner.

The toxicities were, not surprisingly, there, especially hematologic toxicities. I will say for those of us that use this regimen in practice, we use it a little bit differently than what was done in SWOG 1815, but you can't deny that there were significantly higher grade 3-5 toxicities with anemia neutropenia and thrombocytopenia, though the treatment discontinuation rate did not differ. I think the next steps are really going to be the ongoing biomarker analyses. The study had archival tissue and prospective blood collection and we know that in the space of cholangiocarcinomas and biliary cancers, molecular complexities absolutely play a role in how patients do and how they respond to therapies. So that's going to be an important next step, I think, for this study.

Dr. Shaalan Beg: Speaking of biomarkers and an impact on GI cancers, the other malignancy where biomarkers are having a much greater impact than other GI cancers is colon cancer. Another year where we continue to see advances in our understanding of molecularly targeted treatments for colon cancer. What caught your eye?

Dr. Rachna Shroff: Well, there were a lot of really interesting studies happening in this space and as a biliary person, one of the first things I got excited about was seeing Abstract 139 that looked at pemigatinib, which is the drug we are very familiar with in cholangiocarcinoma. This was a single-arm phase two study looking at the use of the FGFR inhibitor pemigatinib in metastatic colorectal cancer patients who had FGFR alterations. And so this was a study that was opened through the ACCRU mechanism. It was multicenter with assignment two-stage design and it was specifically for patients with FGF and FGFR-altered metastatic colorectal cancer who had progressed on standard therapies. There was a prespecified interim analysis for futility after 12 evaluable patients and so 14 patients were enrolled in the first stage of the study and evaluated for the primary endpoint of objective response.

What was seen and the study was subsequently stopped is that there was really not much efficacy, there was no evidence of safety signals, but this did not seem to be a very active drug in patients with FGFR alterations with no objective response noted. So, the study was stopped with the recognition that perhaps the FGFR translocation or fusion patient population may be something to explore since they did not look at that in this study.

The other kind of study that I think is really important was important work of Dr. Raghav and colleagues through SWOG. This was SWOG 1613 Abstract 140. This was the first real study that was investigating targeting HER-2 overexpressed and amplified metastatic colorectal cancer who had RAS wild-type tumors. And it was based on, obviously, some early signals of the effectiveness of HER-2 targeting in metastatic colorectal cancer. And this was a large study looking at pertuzumab and trastuzumab in these patients. They were compared to cetuximab and irinotecan, and the initial plan was for a much larger study. Unfortunately, accrual was really slow so the study was really kind of reformatted and a total of 54 patients were randomized, 26 to the trastuzumab arm and 28 to the CetIri or cetuximab and irinotecan arm.

What was seen was that you can absolutely use HER-2 targeting therapies with trastuzumab and pertuzumab in these patients. It was safe and there were some obvious signs of efficacy in terms of overall response rate with an overall response rate of 31% compared to the CetIri arm. Crossover was allowed from the CetIri arm to trastuzumab and pertuzumab. So just that's important to keep in mind when they start to follow out the survival data. But unfortunately, because this study did not accrue, it was stopped early and it's really hard to understand in terms of power calculations the impact of trastuzumab pertuzumab. Of course, we can't talk about this without recognizing that the FDA approval based on the MOUNTAINEER study for tucatinib and trastuzumab came through during GI ASCO. So clearly HER-2 targeting is here to stay in colorectal cancer.

Dr. Shaalan Beg: So technology is advancing every year and it's important that we are aware of these advances and how they impact our patients. Probably one of the most exciting technologies in oncology in general is the evolution of ctDNA. And it's been amazing to watch that field unfold as we understand how to use circulating biomarkers for early detection of cancer, for minimal residual disease detection, even as a biomarker of response.

What caught your eye when it comes to the use of ctDNA in GI cancers, and how do you see this space develop in the next couple of years?

Dr. Rachna Shroff: I completely agree. I think the technology of ctDNA is so incredibly exciting and as somebody who does not actively see and treat colorectal cancer, I'm a little bit envious of my colleagues in that space because the strides that have been made in terms of understanding the utility of ctDNA, especially in colorectal cancer, has just been tremendous and even for the last two to three years.

One perfect example of integrating that sort of technology into treatment paradigms is the PARADIGM trial, Abstract 11, which was looking at the concept of hyperselection of patients with RAS wild-type metastatic colorectal cancer who were on the PARADIGM trial which basically looked at frontline FOLFOX with panitumumab versus bevacizumab in patients with RAS wild type left-sided metastatic colorectal cancer. So, you know, the initial data from PARADIGM had demonstrated a longer median overall survival 37.9 months versus 34.3 months, but very smartly, the investigators had also collected baseline plasma ctDNA in the biomarker component of this study and used a custom panel that looked at gene alterations for hyperselection and that included KRAS, NRAS, PTEN, and extracellular domain EGFR mutations HER-2 and MET amplifications, as well as some fusions like ALK, RET, and NTRK.

And so out of the 802 patients in the full set, 91% - 733 patients - actually had pretreatment samples for ctDNA, which is really in and of itself, I think, tremendous. And when you break it down, about 28% had at least one gene alteration, and that was across each of those different genes that they were looking at. In the 72% of patients who were defined as hyperselected without any gene alterations, the OS was actually longer with panitumumab versus bev, and that actually was independent of sidedness with hazard ratios that kind of ranged from 0.76 to 0.82. And OS was similar or inferior with panitumumab versus bevacizumab again, regardless of sidedness in patients with any of these gene alterations. And so I think it's a really interesting concept that you can use ctDNA to define negative hyperselection rather than looking at left sided and right sided to really help select patients with frontline therapy in terms of using panitumumab versus bevacizumab. And with the speed with which ctDNA can be obtained, this actually seems like something that could be implemented into clinical practice, which is, I think, really the important component of that.

There were a number of other really interesting abstracts. Abstract 5, presented by Dr. Cohen and colleagues, really looked at the kinetics of circulating cell-free DNA and how that kind of relates to minimal residual disease detection rates. And this was in patients with resected stages one through three colorectal cancer. And so, this was a retrospective study, so we have to keep that in mind. And it was multi-institutional in really over 16,000 patients with stages 1 through 3 colorectal cancer. But the complete dataset had about 417 patients and basically the patients' circulating cell-free DNA levels, the total cfDNA, were compared to the ctDNA MRD positivity rates and they looked at very specific time points after surgery. What the authors generally found was that the postoperative cfDNA correlated well with ctDNA positivity and that there was really the ability to see plasma cfDNA levels kind of track and follow with the very specific MRD windows that were being looked at, which really, again, just kind of talks about leveraging this technology in terms of real-world and real-time application and better understanding and informing us of minimal residual disease post what is thought to be curative resection.

The last one that I thought was really interesting in relation to ctDNA was actually looking at anal cancer and following ctDNA in patients who were treated with definitive chemoradiation. This was a study that was looking at 31 patients with anal squamous cell carcinoma who were treated with definitive chemo radiation and underwent ctDNA response. The majority of these patients had stage 3 disease and the majority of them received the standard 5-FU Mitomycin with radiation. The patients had ctDNA testing performed in 25 of these patients at baseline and then a smaller number over the course of time, some during chemoradiation. And then they looked again at 30 days post chemoradiation. And at baseline, 88% of patients had detectable ctDNA with those with stage three disease having numerically higher baseline ctDNA levels.

And basically what they found was that over the course of treatment, ctDNA levels decreased among the patients with detectable ctDNA. And then ctDNA that tested during chemo radiation showed a drop in decline and were going into molecular remission at a time point in which it was subsequently confirmed that they had a clinical complete response. So, the suggestion here is that the time to molecular ctDNA remission was significantly shorter than being able to see that clinical complete response, which suggests that using surveillance ctDNA monitoring could be an earlier response assessment for patients with anal squamous cell carcinoma who are undergoing definitive therapy.

Now, obviously this needs to be confirmed in a larger manner, but again, really suggests that we could be understanding how we're doing with treatment in more of a real-time fashion, which I just think is incredible for those of us who are making sure that we are doing and taking the right approaches for these patients.

Dr. Shaalan Beg: One of the major transformative announcements that took place only a couple of months before the GI Cancer Symposium was the announcement of ChatGPT. And we heard a lot of discussion on how it can be used for improving cancer care, improving drug development, and in general, artificial intelligence and machine learning. We've been hearing these buzzwords for such a long time, to the point that a lot of people are probably just filtering it out and then this tool comes up and it makes it real. And we're seeing different people apply these technologies in different ways. But there is tremendous potential in how this technology can improve clinical trials, drug development, and early diagnosis. And luckily, we had already secured a keynote speaker, Dr. Matthew Lundgren from Nuance Communications, and he was invited to talk about artificial intelligence, machine learning, and how it applies to cancer care.

I'm really curious to hear what your highlights were from his address and how you see this impacting your day-to-day, or just the ecosystem of which we're all part of.

Dr. Rachna Shroff: Yeah, I will say that his keynote was really one of the highlights of the entire meeting for me. And that is coming from somebody who doesn't really know– I know who I'm speaking to, but somebody who does not truly understand the way AI is moving. And so, I was joking with him that it was like AI 101. And I really, really appreciated the way he was able to kind of speak to a crowd that he doesn't normally speak to and help us really understand the way in which artificial intelligence can be integrated into healthcare, and specifically oncology. To me, I think what were the most salient takeaways from his address was really about how this is just a rapidly evolving field and we need to be a little bit ahead of the eight ball when it comes to thinking how we can smartly leverage artificial intelligence like you mentioned, to improve our clinical research efforts, to improve access, and to improve fully integrating AI into our EMR, so that we can really leverage that technology and ensure that we are capturing every potential patient for a clinical trial and be smarter about how we're even approaching things. I mean, I loved him talking about the prior authorizations and that sort of thing, and the ways in which we can decrease the burden on health care providers and really let us focus on the areas that we need to focus on.

The one thing that I thought was a really important point, though, and I think a number of people asked him, was about how using this technology has the potential to create more gaps and disparities and how can we be smart to ensure that we don't broaden those gaps. And I think that is a really important point that we all need to think about because we know that especially when we think through clinical trials, there's already underrepresentation of certain populations and certain geographic regions. And so, I think that was a really important takeaway for me is how can we make sure that we work and partner with those who are creating these technologies to ensure that we aren't taking two steps forward and four steps back.

Dr. Shaalan Beg: It really calls into question how we define productivity and what our value in the entire delivery system really is. And I think from people who are in middle school or high school to people who are in college and even folks who are in the field as you and I are, it's forcing us to rethink what we bring to the table in a way that we've never been challenged to ask that question ever before.

Dr. Rachna Shroff: Absolutely.

Dr. Shaalan Beg: So, thank you very much, Dr. Shroff. This was wonderful. Thank you for sharing your insights with us today. And we thank you and Dr. George Chang, the chair of the ASCO GI Cancers Symposium, and everyone who worked so hard to develop a robust program this year.

Dr. Rachna Shroff: Thank you. It was so wonderful to be able to speak about it. And thank you to all of the attendees for making it such a memorable meeting.

Dr. Shaalan Beg: And thank you to all our listeners for your time today. You'll find links to the abstracts discussed today on the transcript of this episode. Finally, if you value the insights that you hear on the ASCO Daily News podcast, please take a moment to rate, review, and subscribe wherever you get your podcast.

Disclaimer:

The purpose of this podcast is to educate and to inform. This is not a substitute for professional medical care and is not intended for use in the diagnosis or treatment of individual conditions.

Guests on this podcast express their own opinions, experiences, and conclusions. Guest statements on the podcast do not express the opinions of ASCO. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement.

Find out more about today's speakers:

Dr. Shaalan Beg

@ShaalanBeg

Dr. Rachna Shroff

@rachnatshroff

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Disclosures:

Dr. Shaalan Beg:

Employment: Science 37

Consulting or Advisory Role: Ipsen, Array BioPharma, AstraZeneca/MedImmune, Cancer Commons, Legend Biotech, Foundation Medicine

Research Funding (Inst.): Bristol-Myers Squibb, AstraZeneca/MedImmune, Merck Serono, Five Prime Therapeutics, MedImmune, Genentech, Immunesensor, Tolero Pharmaceuticals

Dr. Rachna Shroff:

Consulting or Advisory Role: Exelixis, Merck, QED Therapeutics, Incyte, Astra Zeneca, Taiho Pharmaceutical, Boehringer Ingelheim, SERVIER, Genentech, Basilea

Research Funding: Pieris Pharmaceuticals, Taiho Pharmaceutical, Merck, Exelixis, QED Therapeutics, Rafael Pharmaceuticals, Bristol-Myers Squibb, Bayer, Immunovaccine, Seagen, Novocure, Nucana, Loxo/Lilly, Faeth Therapeutics