[Association between microsatellite instability and clinico-pathological characteristics in sporadic colon cancer]

Currently, colon cancer is a leading cause of cancer death world-wide. It progresses according to three molecular pathways, named suppressor, mutador and methylator. Microsatellite instability is a hallmark of the lack of reparation, of DNA mismatches and it characterizes a subset of colon tumors (unstable tumors, MSI). MSI-H patients (high degree of microsatellite instability) seem to share clinico-pathological differences with MSS (microsatellite stable) and MSI-L (low degree of microsatellite instability) patients. In this study, associations between high degree of microsatellite instability and pathological (location, mucinous content, differentiation grade, stages T3N0, stages II and III) and clinical features (response to chemotherapy, disease-free survival and overall survival) were evaluated.

117 patients with sporadic colon cancer were classified into two populations (MSS/MSI-L and MSI-H) by using PCR and electrophoresis of seven microsatellites, according to the National Cancer Institute recommendations.

MSI-H tumors tended to be located in the right colon (p = 0.022) and were of mucinous histologic type (p = 0.04). No differences in disease-free survival and overall survival between group of stage II and III patients with MSS/ MSI-L and corresponding ones with MSI-H colon cancer were found (p = 0.54, p = 0.37, respectively). Conversely, MSI-H patients with stage II colon cancer had a favourable prognosis (p = 0.027). Nevertheless, response to 5-fluorouracil (5-FU) and leucovorin was similar in MSS/ MSI-L and MSI-H groups (p = 0.38).

MSI-H patients are characterized by certain pathological features; those MSI-H patients with a stage II seem to have a better prognosis than MSS/ MSI-L patients.