Utility of ctDNA to Manage Adjuvant Therapy in CRC Based on Results of the GALAXY Study - Episode 4

GALAXY: Disease-Free Survival by Stage and ctDNA Status


Stacy A. Cohen, MD, and Mark Lewis, MD, comment on disease-free survival rates by ctDNA status in patients enrolled in the GALAXY study.


Mark Lewis, MD: Here I will note we are looking at all stages, so this is a huge outcome cohort, 1040 patients. When you get to that size, it’s going to allow for a really tight confidence interval. So we are starting to discern some patterns. One thing I noticed, Dr Cohen, I am curious to get your thoughts, is we are starting to see basically a plateau in the ctDNA [circulating tumor DNA] negative groups. If you are ctDNA negative, your disease-free survival really did not decline that much at the 6-month mark vs the 12-month mark, and I thought that was quite compelling. Admittedly, this is not years' long follow-up, this was I think a median of just a little bit over 11 months, but what are your takeaways here?

Stacey A. Cohen, MD: I think it parallels what we have seen in some other studies, which is that first negative time point seems to be a very reasonable predictor. Interestingly, the ctDNA that’s drawn prior to surgery does not seem to inform long-term outcome, which you would think [it would], because typically we use that as a way of demonstrating what is and is not a valuable biomarker. But the initial time point around 4 weeks, as done in the study, does seem to be fairly prognostic of how patients will do over time. And it does hold up, which is why the 6-month and 12-month disease-free survival is fairly similar. I think this is very compelling and mirrors a lot of the data that we have seen previously.

Mark Lewis, MD: Thank you for that. One thing I understand the investigators were doing here is they were going for magnitude. This is a big cohort, which for better or for worse contains stage 1, contains low-risk stage 2, and even contains stage 4. What I would like to do is go to the next slide because here we are getting down to disease-free survival in the pathologic stage 2 and 3.

Here we have a large hazard ratio, albeit with a smaller sample size. What that suggests to me is this is an in jeopardy subpopulation that’s being enriched by people who we know might traditionally be offered adjuvant chemotherapy. And here again I will point out we are seeing a plateau in the negative group, whereas we are seeing a downward trajectory in the positive group. Dr Cohen, any points to make here?

Stacey A. Cohen, MD: No. I think you bring up the same conclusions that I had. Once you take out what presumably would be best acting stage 1 patients and potentially the worst acting stage 4 patients, though of course we don’t know on an individual level, we do see improved outcomes here to some degree. Again, this is the population we think we might most heavily be able to influence with adjuvant therapy.

Mark Lewis, MD: Very well said. With that, let’s finally get to the titular dynamics.

Transcript edited for clarity.