Poorly differentiated colorectal cancers: Correlation of microsatellite instability with clinicopathologic features and survival

Objectives: To evaluate the association of microsatellite instability (MSI) with clinicopathologic features and oncologic outcomes in patients with poorly differentiated colorectal cancer (PD). Methods: Study patients were divided into well-differentiated colorectal cancer (WD) and PD, which were compared according to histologic differentiation and MSI status. Results: Among 1,941 patients, PD was more frequent among microsatellite-unstable tumors (23.6%) than among microsatellite-stable (MSS) tumors (4.2%, P < .001). Patients with PD had worse 4-year overall survival rates than patients with WD (78.6% vs 88.2%, P = 0.010). Compared with MSS-PD tumors, MSI-PD tumors were characterized by right-colon predilection, larger size, and infrequent lymph node metastasis (P < .001 to P = .007). Conclusions: The clinicopathologic characteristics of PD were closely associated with those of MSI. The outcomes of MSI-PD tumors were better than those of MSS-PD tumors, but this finding did not reach statistical significance.