Development of BRAF V600E Mutation in NRAS Q61L Mutated Rectal Cancer.

BRAF and NRAS are oncogenes in the RAS/RAF/MEK/MAP-kinase signaling pathway. Coexistent mutations of BRAF and NRAS in a single colorectal cancer patient have always been considered mutually exclusive or at least rare. The clinical outcome of these patients remains undetermined. Herein we report a 53-year-old man harboring an NRAS Q61L mutation in his primary rectal carcinoma, who presented with a concomitant mutation of BRAF V600E in his liver metastasis biopsy 55 months after the primary CRC surgical resection. Our findings suggest that a BRAF and NRAS developed co-mutation may lead to a distinct clinicopathological progression. BRAF-mutated CRCwill not benefit from anti-RAS targeted therapy.