A Systematic Analysis of Oncogene and Tumor Suppressor Genes for Panitumumab-Resistant Rectal Cancer with Wild RAS Gene - A Case Report

A 58-year-old man was admitted with the complaint of bloody stools. Colonoscopy and computed tomography revealed a rectal cancer with a liver metastasis and multiple lung metastases. After administering a regimen comprising 3 courses of XELOX plus bevacizumab chemotherapy, the sizes of the primary and metastatic lesions decreased remarkably. Abdominoperineal resection was performed for local control of the cancer; the specimen from the initial tumor was found to be KRAS wild type. After 14 courses of XELOX chemotherapy, brain metastases were detected. Although 3 courses of IRIS plus panitumumab were administered, the liver, lung, and brain metastases spread rapidly. A comprehensive genomic analysis focused on cancer-related genes with CancerPlex®found a mutation of the BRAF gene(I326V). BRAF is a downstream molecule of KRAS in the RAS-RAF-MAPK pathway. Therefore, this mutation of the BRAF gene has the possibility of causing resistance against panitumumab that was found in this case. Furthermore, we expect that the systematic analysis of oncogene and suppressor oncogenes will enable us to choose the optimal regimen of chemotherapy or molecular targeting therapy for each patient with colorectal cancer.