Dr. Ahn on Left- Versus Right-Sided Tumors in CRC

Daniel H. Ahn, DO, an oncologist, internist, and assistant professor of medicine at Mayo Clinic, discusses left- versus right- sided tumors in colorectal cancer (CRC).

A lot of the data that have been released over the past 3 years have underscored the fact that the sidedness of a tumor does matter, says Ahn. It is worth noting that there are differences in genomic alterations associated with tumor sidedness. Right-sided tumors tend to be associated with BRAF V600E mutations and a higher prevalence of KRAS mutations, while left-sided or rectal tumors tend to have a higher incidence of HER2 alterations.

Some other genomic alterations are also coming into play, says Ahn. Notably, the data from the CALGB/SWOG 80405 study showed that the sidedness of CRC tumors does matter in terms of sequencing treatments, adds Ahn. Specifically, in right-sided tumors, patients should receive anti-VEGF monoclonal antibody therapy prior to anti-EGFR monoclonal antibody therapy and it is known that these patients can experience a potential prognostic effect with sequencing these agents. However, for the left-sided tumors, that data are not as clear, concludes Ahn.