[A Case of Metastatic Colon Cancer Dramatically Affected by Anti-EGFR Antibody Therapy]

RAS mutation is an established predictive biomarker of resistance to anti-epidermal growth factor receptor(EGFR)therapy in metastatic colorectal cancer. In addition, previous studies identified mutations in ERBB2, FGFR1, PDGFRA, BRAF, MAP2K1, PTEN, and PIK3CA as potential mechanisms of resistance to anti-EGFR therapy. Testing for these mutations might be necessary to determine eligibility for anti-EGFR therapy in patients with metastatic colorectal cancer. CancerPlex®is a nextgeneration sequencer for 413 cancer genes. An analysis panel includes genes that may be associated with resistance to anti- EGFR therapy. A 65-year-old man with unresectable rectal cancer, multiple lung metastases, and a bulky liver metastasis was evaluated for expression of genes associated with resistance to anti-EGFR. The analysis found that all genes indicating resistance were wild-type genes. Cetuximab monotherapy was administered after rectal resection, with dramatic shrinkage of the metastatic tumors. A more accurate selection of patients according to tumor genetic status using CancerPlex®might improve the risk-benefit profile of anti-EGFR therapy.