JCO PO author Dr. Mohamed Salem shares insights into his JCO PO article, “Landscape of KRASG12C, Associated Genomic Alterations, and Interrelation With Immuno-Oncology Biomarkers in KRAS-Mutated Cancers” and the article’s findings of a large-scale, pan-cancer genomic characterization of KRASG12C. Host Dr. Rafeh Naqash and Dr. Salem discuss KRASG12C mutation, KRASG12C -mutated tumors and comutation with STK11 and KEAP1. Click here to read the article!  
TRANSCRIPT

Dr. Abdul Rafeh Naqash: Hello and welcome to JCO Precision Oncology Conversations, where we bring you engaging conversations with authors of clinically relevant and highly significant JCO PO articles. I'm your host, Dr. Abdul Rafeh Naqash, Social Media Editor for JCO Precision Oncology and assistant professor of Medical Oncology at the OU Stephenson Cancer Center.

Today I'm thrilled to be joined by Dr. Mohamed Salem, Gastrointestinal Medical Oncologist, and Research Director at the Levine Cancer Institute in Charlotte, North Carolina. Dr. Salem is the lead author of the JCO Precision Oncology article ‘Landscape of KRAS^G12C, Associated Genomic Alterations, and Interrelation With Immuno-Oncology Biomarkers in KRAS-Mutated Cancers’.

Our guest’s disclosures will be linked in the transcript.

Dr. Salem, welcome to our podcast, and thank you for joining us today.

Dr. Mohamed Salem: Thank you for having me. A pleasure and honor.

Dr. Abdul Rafeh Naqash: For the sake of this podcast, we'll be referring to each other using our first names. So thank you for coming on to our podcast and discussing this very interesting paper. And one of the reasons why we decided to incorporate this is because, as you very well know, KRAS is one of the most common altered genes in cancer, and I'm pretty confident and sure that oncologists, whether it's academic oncologists or community oncologists, have treated patients in different settings having tumors that harbor KRAS alterations. So give us a little bit of a background on where KRAS alterations stand currently and where is drug development in the space of KRAS to give our listeners some idea of why we're interested in this gene.

Dr. Mohamed Salem: Sure, thanks again for having me. And as you mentioned, KRAS mutation happens to be, I think, by far the most common oncogenic mutation we see in oncology and solid tumors. The problem with KRAS is that, for a long, long time, there was very much nothing we could do about it; it was, in fact, called an undruggable target. Until recently, we started to realize this might not be true, and, in fact, we start to see successful efforts trying to target KRAS mutation. Currently, there are several KRAS inhibitors. I think it started with G12C. I personally don't think there was anything specific about G12C, but it just happened to be one of the first targets that we were able to approach. And the initial result from using anti-G12C therapy that was published in the New England Journal of Medicine, I think, a year ago now, showed this is feasible and perhaps effective.

Dr. Abdul Rafeh Naqash: Thank you so much, Dr. Salem, for that explanation. And being a Phase I trialist, I personally have seen a lot of exciting combination-based approaches in the setting of KRAS-altered tumors, especially KRAS^G12C.

Now, specifically delving into your paper, given the extensive length and breadth of data that you've covered here, could you tell us a little bit about why you decided to use KRAS as an interesting topic for your study and the kind of data set that you chose to explore this question?

Dr. Mohamed Salem: What happened once we started to realize how important it is to figure out which KRAS mutation we're dealing with because, at least in colorectal cancer, it's a very common mutation, almost like 40-50% of patients with colorectal cancer tumors carry KRAS mutation. Until very recently, we really didn't pay close attention to which variant it is. Is it KRAS G12D, 13, or G12C? And so on and so forth. And the reason we didn't really pay much attention to that is because there was nothing to do about it; whether the patient has this or that variant was really nothing therapeutically wise it really didn't have an impact. But once we started to realize now there is a therapeutic option and, in fact, now there is a change in the way we think about KRAS mutation, there is a proof of concept that we actually can target KRAS mutation, we started to pay closer attention to this.

And I think this was a paradigm shift in our thinking. So for patients who have KRAS mutation, now we have data showing that KRAS^G12C is something we can target, whether with single agent or with combination therapy. But it was a new era for us because most of us realized it's not going to stop there. It’s not going to be just G12C; I think G12C is the tip of the iceberg, and likely the science is going to go forward, try to target the other variants. So one of the obvious questions was what are the other variants and how commonly those exist, and which tumor types also carry those variants. Because as we were talking before the recording for Phase I, now it is not like one approach fits all; it started to kind of like focus on either molecularly driven or disease-type approaches. And it was very important for us to try to figure out, okay, which tumor type carries the most KRAS variants and, within that tumor, which variants are the most common. And this is what we're trying to answer in this paper.

Dr. Abdul Rafeh Naqash: Thank you so much, Mohamed. I looked at your data set that you had access to, very large data set of around 79,000 tumor samples and close to 14,000 KRAS mutated tumors. Could you tell us a little more about this data set and how you started with looking at the distribution of KRAS across different tumors, and what were the kind of interesting results that you came across as far as KRAS distribution is concerned?

Dr. Mohamed Salem: It's very obvious to all of us now that the field is moving from one size fits all to a targeted approach or treatment target approach. And this is very important and very interesting because usually, when we do that, we achieve better outcomes and lesser toxicity. But the problem that comes with this is that none of us, as a single, even two centers, will have enough data to ask and answer questions. And when you are talking about something like MSI-high or BRAF or KRAS, usually it becomes very challenging for one single institution, doesn't matter how big they are, to try to answer either prevalent or therapeutic approaches. Because of that, most of us now start to understand that cooperation is very important across centers and also across nations.

So, like as you see here in this paper, there was a global cooperation between investigators in the U.S. and in Europe and Austria, and other countries. And what we did as a group we worked with one of the third-party profiling companies. Our group tried to answer what is the prevalence, just a very simple question, what is the prevalence of KRAS mutation, and what is the prevalence of each variant type in each tumor? And none of us could have answered that question on their own. Because of that, we actually collaborated with one of the third-party companies that do next-generation sequencing for tumors, and we were able to collaborate with them to have access to that database and answer some of those questions.

Dr. Abdul Rafeh Naqash: Excellent. As everybody knows, NGS is a standard of care testing that oncologists do, especially for advanced settings, to identify driver alterations or therapeutic interventions that may be relevant for patients. So in this data set, it seems you had access to NGS data, tumor mutational burden, and PD-L1 data for these tumor types. Could you tell us about the differences in the distribution for KRAS and the KRAS subtypes that you identified in this data set?

Dr. Mohamed Salem: Sure. So, as you mentioned, we looked actually at almost 79,000 tumor samples that underwent next-generation sequencing by our collaborator. And it appears that about 17% of the tumors or so had some kind of KRAS mutation. And then, after that, we start to see G12C when we start looking at each variant. G12C were about 11%, 12%, and about 88% of the remaining KRAS mutant tumors harbored some different kind of KRAS mutation.

The next question was, in general, in all tumors, what was the most common KRAS variant seen? I think it mimicked what was already out there. It appears that G12D happened to be perhaps the most frequent mutation seen in KRAS mutation tumors, followed by G12V, followed by G12C, and then G12/13, and then others. What was very interesting, actually, an observation we saw, is that we were able to realize the distribution of KRAS variants varies according to the tumor subtype. So, for example, in pancreatic cancer, we could see patients who had G12R KRAS mutation variants. This was not seen commonly in other tumors. And the reason that's important is because maybe that will be something in pancreatic cancer tumors that will be worth looking at and do therapeutic approach there. But also, I'm sure you're already dealing with this in your clinic quite often. It was interesting, obviously, that non-small cell lung cancer was the most common organ that actually carries G12C, followed by colorectal cancer; followed by a very interesting actual observation that was very interesting for us to see was in appendiceal cancer. As you know, appendiceal cancer is not a common disease; it's a relatively rare disease. And we were surprised to see some of them actually have G12C mutation. And again, the reason that's important is that it just opens the door for possible therapeutic options and in context of clinical trials.

Dr. Abdul Rafeh Naqash: Excellent. Definitely, the advantage of having such a rich data set like you did enabled you to look into some of these unique distributions across rare tumors, which makes it very interesting.

Now, one thing that I realized in the paper is that these tumors of unknown origin, where you identified or your group identified that they had a certain percentage of KRAS alterations, suggesting maybe their tumor of origin is perhaps lung or upper diaphragm, which could have therapeutic implications. Could you tell us a little more about this?

Dr. Mohamed Salem: Yeah, this was another very interesting observation we saw because it is not uncommon for us in the clinic, we get like a cancer biopsy, but we cannot tell where it's coming from. And there are multiple ongoing efforts to try to identify that for the obvious reasons. But it was very interesting when we looked at those groups that when you had cancer adenocarcinoma but of no identified origin, it was the fourth common tumor that we see G12C. I think if you can just make the assumption - I don't think we have proved that - but since lung cancer was the most common tumor that exhibited G12C mutation, and now we have tumors of unknown origin also, many of them exhibit G12C mutation, we thought this could be a lung primary. As you know, there are also now a few platforms trying to identify the tumor origin based on the agent sequencing, but we didn't try to associate it with that.

Dr. Abdul Rafeh Naqash: Thank you for that explanation. Now, one of the other things I observed is you tried to delve into smoking status, very interestingly, and how that correlated with KRAS alterations. And as we know, lung cancer, obviously there is a strong predilection in patients who are smokers, but irrespective of smoking, there can be other alterations that drive lung cancer. But interestingly, in your paper, you identified a unique correlation between smoking and G12C and also found out something on those lines in colorectal cancer, which, to my understanding, has not been described before. What is your understanding of why that happens? What could be the mutational events that lead to something like that, and how could that be potentially therapeutically exploited?

Dr. Mohamed Salem: I think this was one of the very interesting findings we observed. And you are right; just because the nature of lung cancer, we know many of patients are either active smokers or former smokers. So it was not a surprise for us to see that there is some kind of association with smoking status and lung cancer. But to your point, what was really surprising and, in a way, interesting for us to see, actually, that association for patients with colorectal cancer. Smoking actually happens to be one of the risk factors, like in colon cancer, but obviously not as high as lung cancer. But when we looked at the data, demographic, and clinical features, it was obvious actually that current smoking status, whether a current smoker or prior smoker, had an association with G12C. And also, with gender as well, females tend to have more G12C, or G12C mutation was more likely to be seen in females than males. So the fact that we were able to identify the smoking status and gender as more likely to harbor G12C mutation was interesting.

I have to tell you, the reviewer, when we submitted the paper for review, the reviewer came back and asked us, did this happen just because you had too many lung cancer, and most lung cancer patients smoke, that's why you're seeing that association? And we went back and looked at the data again and spoke with our biostat team in the study, and we were able to actually run the analysis and show that, no, it is not just because of the enrichment; it's actually a real association between the smoking status and G12C. It's very interesting to see, at least in colorectal cancer, it's following the same trend in lung cancer.

Dr. Abdul Rafeh Naqash: Right. And one of the other things I remember when I was reading through your paper and smoking status, I remembered this paper that was published in Science Magazine 2016, looking at how mutational burden changes in patients that have a history of smoking. But when you connect the dots here, interestingly, it seems like, especially in lung cancer, from what you guys have described here, is that the smoking status impacts what kind of KRAS alteration is present. But at the same time, you didn't see a tumor mutational burden that was significantly higher in G12C, mutated non-small cell lung cancer, where you would expect a lot of these G12Cs to be related to smoking. But on the other hand, the tumor mutational burden was not necessarily increased. And I understand you may not have an explanation for that through the data that you've published on, but that was kind of an interesting observation that I had. I don't know if you have any specific comments on that.

Dr. Mohamed Salem: No, it's absolutely correct. What we thought is that we should see that because the obvious rationale is just cited, but it wasn't. And until today, we're actually trying to figure out why the disconnect because you have people who smoke usually you expect like PD-L1 is positive, you expect higher tumor burden, but it didn't show at least a statistically significant correlation.

Dr. Abdul Rafeh Naqash: Thank you. And I guess it's notable to mention that you did have some interesting correlations for tumor mutational burden overall, and with PD-L1. Could you tell us about that for different KRAS genetic alterations?

Dr. Mohamed Salem: There were few papers published before by our colleagues trying also to understand the correlation between G12C mutation and immunostatus or immune microenvironment and some biomarkers. And I think, at least to my understanding, there was not one consensus. I think it was different findings to some degree. So, in general, when we actually looked at the entire cohort, regardless of the tumor type, it appears that tumors that carry G12C mutation also happened to have higher PD-L1 expression. What was very interesting was that once we started to look at different tumor types, this was not seen across all tumors. So some tumors did actually carry that, and some other tumor types didn't show that correlation. And to be honest with you, I'm still, until today, I'm not sure why. Is this just a function of number, or actually there is more tumor biology that reflects that? I have to say my own feeling, and that's something we need to study further, is that I think it is tumor biology. One thing was also very interesting to us from the clinical side. You have G12C mutation in lung, and you have G12C mutation in colorectal, and in the New England Phase I study, you could see very clearly that targeted G12C is more effective in the lung compared to colorectal. It's the same target, the same drug, yet the response is different once you start to have two different tumor types. So that just got me to think there must be something with the tumor type and microenvironment of the tumor and also associated co-mutations and other factors that impact that.

Dr. Abdul Rafeh Naqash: I couldn't agree with you more, and I totally have seen that in some of the work that has been published or data that I've been part of where different tumor biology, the tumor microenvironments, even sites of metastasis make a difference in how a certain mutation behaves. So definitely something that needs further validation with perhaps proteomic and transcriptomic data to understand functional characterization of the downstream consequences for some of these mutations. And you pointed out co-mutation status. That's an ever-emerging question for some of the potentially druggable alterations, whether combination approaches targeting some other co-occurring common co-mutation would have more benefit. Could you tell us about some of the unique, interesting commutations that you identified in your cohort that were more common in certain KRAS subtypes?

Dr. Mohamed Salem: Sure. I think that's also something we try to look at for the reason I just mentioned. We know that tumor origin and tumor type influence response and sensitivity to therapy. I think the best example we have, at least in colorectal cancer, is the BRAF mutation. When we saw the BRAF inhibitor having very nice response rate and control of BRAF mutant melanoma in colorectal cancer, we saw that it’s going to be the same thing, the same drug, the same target, same thing’s going to happen. And obviously, it was not the case. And this was a lesson for all of us to understand. Even if it is the same target, even if it's the same drug, tumor origin matters, and that’s likely because of the associated co-mutations that will influence the pathway of the tumor and perhaps either the sensitivity to the drug or maybe resistance to the drug.

So it was very important for us to look also at the associated co-mutations. And I think one of the KEAP1, and perhaps you will comment on this more than me, but the KEAP1 gene was likely to be mutated in those tumors who have G12C mutation than others. Another one was STK11. And there were a few other ones, it depends on which tumor type, but KEAP1 was a very interesting finding for us too. Because as you're aware, it's important, at least in lung cancer, and maybe will impact therapeutic approach too.

Dr. Abdul Rafeh Naqash: You're definitely right. It is important in lung cancer, and there's data that has shown both the STK11 and KEAP1 tumors have inferior outcomes to checkpoint inhibitors and are partly involved in metabolic reprogramming of the tumors. So there's definitely emerging targets that are trying to see if combination approaches in STK11 mutant lung cancer will demonstrate some level of benefit. But I think the co-mutation status would potentially have some sort of impact. But again, functional studies that help us understand what are the downstream consequences of one mutation versus another need to be further performed to get a better understanding of this space.

But I think this is definitely interesting work and very interesting results. Hopefully, our listeners will feel the same and maybe even try to go through the paper to understand some of the other additional results that you have published as part of this extensive paper.

We thank you on behalf of JCO Precision Oncology for submitting your work to JCO Precision Oncology, and hopefully, you'll consider us for further subsequent work in this space. Thank you so much for being with us today.

Dr. Mohamed Salem: No, thank you for having me, and actually, on behalf of my co-authors, I also wanted to thank JCO Precision Oncology for their interest in our paper. And, of course, for the reviewers, because there was no doubt they actually made our paper a much better one. So thank you for having me today, thank you for the entire team.

Dr. Abdul Rafeh Naqash: Reviewers definitely remain the people hidden behind the scenes who help in getting work refined and eventually published. So thank you again.

And thank you for listening to JCO Precision Oncology Conversations. Don't forget to give us a rating or a review, and be sure to subscribe, so you never miss an episode. You can find all ASCO shows at asco.org/podcasts

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.

Guest Bio

Mohamed E. Salem, MD, is Research Director, Associate Professor of Medicine, and Gastrointestinal Medical Oncologist in the Department of Solid Tumor Oncology at the Levine Cancer Institute.

Guest Disclosures (See also: Landscape of KRAS^G12C, Associated Genomic Alterations, and Interrelation With Immuno-Oncology Biomarkers in KRAS-Mutated Cancers)

Mohamed Salem:

Consulting or Advisory Role: Taiho Pharmaceutical, Exelixis, Bristol-Myers Squibb, QED Therapeutics, Novartis, Pfizer, Daiichi Sankyo/Astra Zeneca, Merck

Speakers' Bureau: Taiho Pharmaceutical, Daiichi Sankyo/Astra Zeneca, BMS, Merck, Pfizer

KRAS Variants, G12C, TMB, high PD-L1 Expression in Solid Tumors

JCO Precision Oncology Conversations