Genomic overview of right-sided and left-sided colorectal cancer using comprehensive genomic sequencing.

Abstract

e15101 Background: Although the difference in right vs. left sidedness of colorectal cancer (CRC) in response to targeted therapy has been reported, we hypothesized that right-sided colorectal cancer (RCC) is more likely to have genetic alterations associated with resistance of anti-EGFR therapy. We tested this hypothesis using comprehensive genomic sequencing (CGS) on a set of samples from well-characterized CRC patients. Methods: Two-hundred-one primary colon cancer patients with either RCC or left-sided colorectal cancer (LCC) were analyzed. We investigated gene alterations using 415 gene panel, which includes the gene alterations associated with resistance of anti-EGFR therapy: TK receptors ( ERBB2, MET, EGFR, FGFR1, and PDGFRA), RAS pathway ( KRAS, NRAS, HRAS, BRAF, and MAPK2K1), and PI3K pathway ( PTEN and PIK3CA). We defined the patients who had no alterations in any of the genes as “all wild-type”, who are theoretically considered as responders of anti-EGFR therapy. Other patients with genetic alterations in resistance pathways were defined as “mutant-type”. Results: Fifty-six patients (28%) and 145 patients (72%) had RCC and LCC, respectively. Mutation of PIK3CA, BRAF, ACVR2A, MSH6, and CTNNB1 were significantly associated with RCC. Conversely, mutation of APC and TP53 were significantly associated with LCC. Regarding the gene alterations associated with anti-EGFR therapy, only 6 of 56 patients (11%) of RCC were “all wild-type”; in contrast to 41 of 145 patients (28%) of LCC that were “all wild-type” ( P = 0.009). In 45 Stage IV patients treated with anti-EGFR therapy, RCC showed significantly worse progression-free survival (PFS) than LCC ( P = 0.019), and “mutant-type” RCC showed worse PFS compared to the others ( P = 0.018). Conclusions: RCC is more likely to have the genetic alterations associated with resistance of anti-EGFR therapy compared to LCC. Primary tumor sidedness is a surrogate for the non-random distribution of molecular subtypes in CRC.