132 Background: Colorectal cancer (CRC) is the second leading cause of cancer-associated deaths in the United States. Some of the poor prognostic factors for metastatic CRC (mCRC) include BRAF V600E mutation and microsatellite instability (MSI) that result from mutation or loss of mismatch-repair genes. While the prognostic value of MSI-high CRC for early-stage patients treated with resection and adjuvant chemotherapy is favorable, the prognostic value of BRAF mutation is still unclear. Furthermore, the impact of BRAF mutation with concurrent microsatellite instability on overall survival has not been well investigated. Methods: Here, we collected BRAF mutation status and MSI status of stage II/III CRC patients (n=106) treated at the University of Kansas Cancer Center between September 2009 and July 2020 and compared overall survival between 4 subtypes:MSI-H/BRAF mutant (n=16), MSS/BRAF mutant (n=4), MSI-H/BRAF WT (n=17) and MSS/BRAF WT (n=69), further stratifying patients by age at diagnosis and tumor location. Molecular data were obtained from molecular oncology laboratory as PCR or IHC-based or acquired from outside records. Subgroup analyses were done for stage II and stage III cancers. Results: Table shows the patient characteristics. From our preliminary analysis, MSI-H CRC was found to be primarily a right-sided tumor (MSI-H/BRAF mutant: 94% and MSI-H/BRAF WT 76%). On the contrary, MSS CRC had a more heterogenous localization, spanning left colon, right colon and rectum. In our patient cohort, median survival was not reached for stage II patients whereas for stage III patients, BRAF mutation was associated with poor median survival irrespective of MSI status (MSS/BRAF mutant: 27 months and MSI-H/BRAF mutant 29 months). Median overall survival was found to be 87 months, not reached, 27 months and 29 months for MSS/BRAF WT, MSI-H/BRAF WT, MSS/BRAF mutant and MSI-H/BRAF mutant, respectively. Although associated with poor survival, MSI-H/BRAF mutant displayed later age at diagnosis (mean age 73) compared to MSS/BRAF mutant (mean age 60, p-value<0.029). Conclusions: Our finding suggests that BRAF mutation has poor prognosis even at earlier stages of the disease and that MSS/BRAF mutation, in particular, has the worst prognostic features. These findings highlight the need for BRAF-targeted therapy for CRC at any stage. Due to small sample size, however, our results warrant validation in a larger cohort. [Table: see text]
Combination of microsatellite instability and BRAF mutation status for subtyping colorectal cancer