Prognostic relevance of microsatellite instability in pT3N0M0 colon cancer: a population-based study

Although surgery alone represents a curative approach for patients with pT3N0M0 colon cancer, about 15-20% of these patients develop a relapse of disease. Microsatellite instability (MSI) is one of the most important molecular markers in colorectal cancer. The aim of this study was to investigate the prognostic relevance of MSI in all pT3N0M0 tumors recorded in the Cancer Registry of the Province of Modena--(Northern Italy) within the 2002-2006 period in patients who showed a relapse of disease during the 5-year period of follow-up (59 cases). They were compared to 59 controls similar in clinical and pathological features but with good prognosis. None of the subjects received adjuvant chemotherapy. MSI status was tested using BAT25, BAT26, NR24, and CAT25 fluorescent-labeled mononucleotide markers. The overall prevalence of MSI was 12.7% (15 of 118 cases). MSI was detected mainly in mucinous adenocarcinoma (p < 0.003), in high-grade tumors (p < 0.008), in right-sided neoplasms (p < 0.005), and in patients with a better prognosis, though the difference was not statistically significant (11/59 patients -18.6% vs 4/59 patients -6.7%; OR 0.36 CI 95% 0.11-1.15; p = 0.08). However, in multivariate analysis, MSI status becomes the strongest independent factor associated with relapse (OR 0.21, CI 95% 0.06-0.81; p = 0.023), together with mucinous histological type (OR 0.40, CI 90% 0.18-0.92). MSI is a relevant prognostic factor in stage pT3N0M0 colon cancer suitable to discriminate those patients with a high risk of relapse.