Molecular profiling of the colon cancer in South-Eastern Romania: Results from the MERCUR study

Colorectal cancer is a heterogeneous disease with multiple epigenetic alterations and different molecular features. The molecular classification is based on 2 major distinct pathways: microsatellite stable pathway and the microsatellite instability pathway. Molecular profiling of colorectal cancer provides important information regarding treatment and prognosis. Aim of the study was to assess the frequency of microsatellite instability in colon cancer and the clinicopathological characteristics of the tumors with high level of microsatellite instability (MSI-H) in our region. The secondary outcome was to assess the frequency of v-raf murine sarcoma viral oncogene homolog B1 (BRAF) mutations in colon cancer. The study included 129 patients with colon cancer fit for surgery. Demographic data, clinical and pathological data, immunohistochemistry staining pattern (4 mismatch repair proteins were investigated), and BRAF gene mutations were assessed. According to microsatellite instability status by polymerase chain reaction, patients were divided into 3 groups: microsatellite stable (MSS) = 108 patients, high level of microsatellite instability (MSI-H) = 15 patients and low level of microsatellite instability (MSI-L) = 6 patients. Different clinicopathological comparisons between MSS and MSI-H patients, and between MSS and MSI-L patients were performed. Microsatellite instability was found in 16.3% patients: 11.6% had MSI-H and 4.7% had MSI-L. Significantly more patients in the MSI-H group than in the MSS group were female (P = .01) and had a family history of colon cancer (P < .001). MSI-H and MSI-L groups were associated with the ascending colon location of the tumors, were mostly type G3, T2, and stage I whereas MSS tumors were mostly G2, pT3, and stage III. Overall, BRAF mutations were identified in 18/129 patients (13.9%). BRAF mutant tumors were predominantly associated with MSI-H and MSI-L tumors. Immunohistochemistry had a sensitivity of 76% and a specificity of 89% in detecting MSI tumors and an accuracy of 87.6%. The frequency of microsatellite instability in our study was 16.3%. MSI-H is a distinct molecular phenotype of colon cancer with particular features: female gender, family history of colorectal cancer, a predilection for the ascending colon, poorly differentiated, predominantly T2, and stage I. The frequency of BRAF mutations was 13.9% and mutations were more often present in the MSI tumors.