Microsatellite instability is inversely associated with type 2 diabetes mellitus in colorectal cancer

BACKGROUND: Microsatellite instability (MSI) is a clonal change in the number of repeated DNA nucleotide units in microsatellites. High-frequency MSI (MSI-H) colorectal cancers (CRCs) are known to have different clinicopathological features compared with microsatellite stable (MSS) CRCs. In addition, previous studies have shown that type2 diabetes mellitus (T2DM) is a risk factor for malignant tumors including CRCs. The aim of this study was to investigate the relationship between T2DM and MSI-H colorectal cancer. METHODS: The study design is a single center, cross-sectional study. Data from a series of 936 patients with CRCs were collected and MSI status was assessed. RESULTS: In total, 29 (3.1%) and 907 (96.9%) tumors were classified as having MSI-H and low-frequency microsatellite instability or being MSS (MSS), respectively. Of the 936 patients, 275 (29.6%) were associated with T2DM. One (3.4%) of the 29 MSI-H patients and 274 (30.2%) of the 907 MSS patients had T2DM. Thus, the incidence of T2DM was significantly less frequent in MSI-H compared with MSS patients (Fisher’s exact test: p = 0.0007). CONCLUSIONS: We conclude that MSS tumors are significantly more common than MSI-H tumors among individuals with T2DM.