So which interpretation is right?

It’s not just SIRT and bacteria who are clinging to the right side of the colon. A post-hoc analysis of the 2014 PETACC-8 trial--designed to assess a benefit with the addition of cetuximab to FOLFOX for resected Stage III colon cancer (if you haven’t heard of it, it’s because there wasn’t one)--looked at whether the sidedness of the primary tumor site influenced outcomes. As expected, across all enrollees, left-sided tumors conferred a better 5-year overall (though interestingly not disease-free) survival than right-sided ones. Unexpectedly, looking at only RAS-mutant colon cancers, it was the right side that prevailed with a significantly longer disease-free (but not overall) survival time. And this was regardless of treatment arm (i.e., cetuximab consistently added no benefit). The takeaway? Besides cetuximab being a reliable let-down, primary tumor location matters and in more complex ways than we thought. After all, the idea that there are different biologic environments across different sites along one of our longest internal organs, well, just seems right.