May 26, 2022
Dr. Shaalan Beg, of UT Southwestern’s Harold C. Simmons Comprehensive Cancer Center and Science 37, discusses hot topics in GI oncology, including KRAS wild-type pancreatic cancer, the SURF-Cohort trial in hepatobiliary cancer, and key studies in gastric cancer featured at the 2022 ASCO Annual Meeting.
Transcript
ASCO Daily News: Hello and welcome to the ASCO Daily News podcast. I'm Geraldine Carroll, a reporter for the ASCO Daily News. My guest today is Dr. Shaalan Beg, who is an adjunct associate professor and gastrointestinal (GI) medical oncologist at UT Southwestern Harold C. Simmons Comprehensive Cancer Center.
Dr. Beg also serves as vice president of oncology at Science 37. Dr. Beg will be telling us about key posters in GI oncology that will be featured at the 2022 ASCO Annual Meeting. His full disclosures are on our show notes and disclosures of all guests on the podcast can be found on our transcripts at asco.org/podcasts.
Dr. Beg thanks for coming on the podcast today.
Dr. Shaalan Beg: Thank you so much for having me.
ASCO Daily News: Let's begin with “A multicenter, non-randomized, controlled trial to evaluate the efficacy of surgery versus radiofrequency ablation for small hepatocellular carcinoma (SURF-Cohort Trial): Analysis of overall survival.” That's Abstract 4095. This study evaluated the efficacy of surgery versus radiofrequency ablation for small hepatocellular carcinoma. So, what are your key takeaways from this study?
Dr. Shaalan Beg: This is a very interesting and timely clinical trial from our investigator colleagues in Japan, Dr. Yamashita, and colleagues, where they evaluated the effectiveness of radiofrequency ablation versus surgery for patients with small hepatocellular carcinomas who have a good liver function.
History is that the best most effective treatment option has always been surgery and we know that ablative techniques like radiofrequency ablation (RFA) or stereotactic radiation can do a good job in controlling the individual cancers, but we don't know what the long-term effects can be in terms of recurrence, free survival, and overall survival.
So, this trial looks to compare RFA or radiofrequency ablation versus surgery for groups of patients who have a good liver function, so a Child-Pugh score of 7 or less, and those who had no lesion greater than 3 centimeters and less than 3 hepatocellular carcinoma (HCC) nodules.
All the people were evaluated by surgeons and hepatologists, to confirm that they would be eligible for both procedures. And then the patients received either 1 of those treatments and they followed them in the long term and found that there was no significant difference between how people who are treated with surgery fared versus RFA.
This is really interesting and practical and timely because the results of these clinical trials can inform our clinical practice today. The median follow-up period was 6.8 years in the surgery group and 6.7 years in the RFA group and the overall survival was not different. Their 5-year overall survival for surgery was 79.7%. And very similar to what they were seeing in both groups.
ASCO Daily News: Excellent! Great to hear some promising developments for this patient population. Well, in Abstract 4026, investigators are suggesting that the choice of PD-L1 immunochemistry assay influences clinical eligibility for gastric cancer immunotherapy. What are your thoughts on this study?
Dr. Shaalan Beg: Yeah! Clinicians, clinical investigators, and even patients have been really confused by the definitions of PD-L1 expression. PD-L1 expression is 1 of our biomarkers for response to immunotherapy and immune checkpoint inhibitors. But the challenge in this field is that there are multiple assays that define various criteria for PD-L1 expression. And if you look at different clinical trials, they look at different definitions of positivity. So, a trial may have 1 plus. Some may have 5 plus percent. Some have 50 plus percent.
So, this group out of Singapore took 362 gastric cancer samples, and they evaluated its PD-L1 expression using the combined positive score or the combined positive score (CPS), the tumor proportion score (TPS), and immune cell expression, and they compared them to see how well all of these performed because what's important to remember is we don't know how interchangeable the different immunohistochemistry (IHC) assays are. We have the Dako 22C3, we have the Dako 28-8, and then the Ventana assays and different clinical trials have used different versions of these at different expression levels. And regulatory bodies haven't really defined how to do the testing.
So, different sites and different physicians, and different practice groups are using different assays and may be interpreting differently. What this trial is telling us is that if you use the Dako 28-8 assay, you identify a much higher proportion of people who are positive for PD-L1, whether you use the 1% cut off or the 5% cut off, or the 10% cut off. Listen to these numbers. 28-8 at CPS of greater than 1, 70% with 28-8, and 49% with 22C3.
If you use the 10% cut-off, it's 13% if you use a 28-8 assay, but 7% for the 22C3 assay. So, that kind of throws into question how these assays are being used in daily practice. Well, some people may be, but a lot of people are not thinking about the cut-offs that were used in those clinical trials, especially when that comes to finding treatment options for our patients. And if we use the 28-8 assay, we’re bound to find more patients who are PD-L1 positive, but that may not be the assay that the trials used in their validation cohort.
So, we may end up treating the wrong patients. But at the same time, if we use the other assay, we may be missing out on people who are PD-L1 positive. So, I think this is a call. This is a call for the field to harmonize how PD-L1 expression is defined. We need more data on inter-assay concordance so we can find the right drug and the right biomarker for the right patients.
This is a call for better prospective data and a call for harmonization between different assays and between different trials because this is an issue that is plaguing clinical practice today.
ASCO Daily News: Thank you! So, let's talk about advances in pancreatic cancer and Abstract 4155. The authors of this study note that pancreatic adenocarcinoma is the fourth leading cause of cancer deaths, with an increased incidence among patients younger than 50 years old. This study is a comparative analysis of the targetable landscape in KRAS mutant and wild-type pancreatic adenocarcinoma. So, can you tell us about it?
Dr. Shaalan Beg: The pancreatic cancer field has really suffered from a lack of effective treatment options, especially targeted treatment options and lack of effectiveness of immunotherapy for this disease.
Most patients still receive chemotherapy and we only have a couple of different combination treatments to help treat this disease, which is increasing in terms of the number of new cases and cancer-related deaths, and by some estimates may be the third leading cause of cancer-related deaths in the U.S.
A big reason that the survival for this cancer has not improved is because we don't have a lot of actionable or targetable mutations for this disease. One of the biomarkers that does have a corresponding treatment option is people who have a BRCA mutation. PARP inhibitors like olaparib have been approved for that group of patients, but the effectiveness of that medicine is modest for this disease, and we still have to see how much it's incorporated into daily practice.
But outside of the BRCA mutations and other DNA damage repair alterations, KRAS is really the most common mutation and there are new drugs that are out there to target KRAS. 90 plus percent of pancreas cancers have KRAS and if you think about it the other way, a small proportion of patients with pancreas cancer don't have KRAS.
So, what this abstract is looking to study is what are the characteristics of patients with pancreas cancer who don't have a mutation in KRAS, and can be the absence of KRAS actually be a biomarker for other mutations and other treatment strategies for pancreas cancer.
And this was a fairly large study of about 5,000 patients with pancreas cancer that use a commercial NGS assay. The same commercial NGS assay, who performed gene analysis, as well as full transcriptome RNA-seq, were retrospectively reviewed. And they found that people who had a KRAS wild-type tumor meaning no mutation in KRAS were much more likely to have mutations in HRD and in BRAF compared to those that had mutations in KRAS.
And then when you look at fusions, there was a much higher rate of NRG fusions. At the 2021 ASCO Annual Meeting, we heard some data on some new agents that are primarily targeting tumors that have fusions in NRG. And what this abstract is telling us is that the absence of a KRAS mutation may indirectly prompt us to look for other mutations, particularly fusions that may have additional treatment options available. So, this indirectly may be a biomarker of other actionable mutations.
The overall proportion of KRAS wild-type in this cohort was 21%. So higher than what I would have expected, but it's 21% out of 5000 cases that they evaluated and they really set out to see if young-onset pancreas cancer folks have a different proportion of KRAS wild-type and the proportion of KRAS wild-type in both young and typical onset pancreas cancer was really the same.
So, I believe this prompts us to think about pancreas cancer in 2 buckets, the KRAS wild-type, and KRAS mutated pancreas cancer. If we ever come across someone who has no detectable KRAS mutation, we should make sure that they have full transcriptomic analysis so we can look and get better coverage on those fusion changes that may have more treatment options associated with them.
ASCO Daily News: I'd like to follow up with a question about Abstract 4130. Investigators analyzed the molecular profile and clinical outcome of a cohort of patients with KRAS wild-type pancreatic ductal adenocarcinoma, what does this study tell us about the treatment implications for these patients?
Dr. Shaalan Beg: Yeah, so this was an abstract by Dr. Aakash Desai from the Mayo Clinic, and they went back and retrospectively reviewed patients who were seen at their center. And they looked for similar questions as the other abstract had done, but this was from a single center, and it seems like people had had multiple different assays performed.
In this cohort, they found 240 patients. That's 8%, had KRAS wild-type disease. So, they found 19 patients who did not have a KRAS mutation. And they went to see if there were any hints of differences or specific mutations between the patients with wild-type and mutated. And they found that the landscape of KRAS wild-type in pancreas cancer was very heterogeneous, and it was difficult for them to generalize or make any statements on what that could suggest.
A couple of things to think about for this study. Well, first of all, I think it's important for us to acknowledge that this particular space, the KRAS wild-type space, is gaining a lot of attention and is being recognized as an independent entity. So, you have multiple abstracts that have looked to study this group of patients.
I think the second study is different from the prior one in that it's a single-center study. And from what I understand, they may have used multiple assays. So, there was less standardization on the actual mutation testing that was being performed. And that has relevance for this specific question because we know that we need deeper transcriptomic analysis in order to be able to perform RNA-seq and really understand the fusions that may be driving cancer, and it's hard to know what the coverage for the mutations that were evaluated in the second abstract, which mutations were really being covered.
But if we take a couple of steps back and look at this, with the lens of where the pancreas cancer field is headed, again, I want to emphasize that how I view these coming together is that KRAS wild-type, pancreas cancer is becoming recognized as its own identity.
ASCO Daily News: Excellent! Well, thank you Dr. Beg for sharing your valuable insights with us today on the ASCO Daily News podcast. It's certainly an exciting time in GI oncology.
Dr. Shaalan Beg: Absolutely! Thank you so much for having me.
ASCO Daily News: And thank you to our listeners for your time today. You'll find links to the abstracts discussed today in the transcript of this episode. Finally, if you're enjoying the content on the ASCO Daily News Podcast, please take a moment to rate, review and subscribe wherever you get your podcasts.
Disclosures:
Dr. Muhammad 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
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