629 Background: Recently, anti-programmed death 1 (PD-1) antibody has shown promising efficacy in a phase II trial for patients with microsatellite instability-high (MSI-H) tumors, especially in those with metastatic colorectal cancer (mCRC). Currently, several clinical trials of anti-PD-1 antibody for patients with MSI-H mCRC are ongoing. However, little is known about the frequencies and clinicopathological features of MSI-H mCRC in Japanese patients. Methods: Patients with histologically confirmed adenocarcinoma of mCRC were eligible for this observational study. MSI status was analyzed in tumors using the MSI Analysis System (Promega) composed of 5 mononucleotide markers. KRAS, NRAS, BRAF and PIK3CA mutations were also evaluated using the multiplex kit. Results: A total of 232 patients were enrolled until August 31, 2015, of which MSI-H was detected in 5 patients (2.1%). Among five patients with MSI-H mCRC, median age was 45 years (28-75), four had tumors on right-sided colon, five had moderately differentiated adenocarcinoma, one had poorly differentiated adenocarcinoma, and three had stage IV disease at presentation. Overall survival for patients with MSI-H mCRC from the start of first-line systemic chemotherapy ranged from 8.1 to 62.0 month. All five patients with MSI-H mCRC had RAS wild-type tumors and two had BRAF V600E mutation. One patient with MSI-H mCRC was enrolled in a phase II trial of anti-PD-1 antibody. Conclusions: MSI-H mCRC is rare in Japanese patients. A large scale nationwide cancer genome screening project together with MSI status is required to evaluate more detailed clinicopathological features and facilitate the enrollment of patients with MSI-H mCRC for clinical trials with anti-PD-1 antibody.
Distinct BRAF (V600E) and KRAS Mutations in High Microsatellite Instability Sporadic Colorectal Cancer in African Americans
