Clinicopathologic Characteristics of Left-Sided Colon Cancers with High Microsatellite Instability

Background: High microsatellite instability (MSI-H) colorectal carcinomas (CRCs) with numerous mutations in the microsatellite sequence are characterized by a fright-sided preponderance, frequent peritumoral and intratumoral lymphocytic infiltration, and frequent mucin production. However, no study has correlated anatomic site and type of genetic changes with clinicopathologic changes. Methods: We analyzed the histopathologic features of 135 MSI-H CRCs and compared them to 140 microsatellite stable (MSS) CRCs. Histopathologic changes in MSI-H were further analyzed according to anatomic sites and genetic changes. Results : MSI-H CRCs showed previously reported clinicopathologic findings; a right-sided preponderance, an increased number of mucinous carcinomas, and peritumoral lymphoid reactions (p<0.001 for each variable). Increased serum CEA levels showed an MSS CRC preponderance (P=0.013). We further analyzed the histologic differences between right- and left-sided MSI-H tumors. We found that MSI-H CRCs on both sides had similar clinicopathologic findings, except for higher tumor stage (p=0.048) and less frequent abnormal CEA levels in left-sided MSI-H tumors (p=0.027). We found that not all clinicopathologic features were different between hereditary nonpolyposis colorectal cancers (HNPCCs) and sporadic MSI-H CRCs. Conclusions These findings indicate that MSI-H CRCs of the left colon have similar clinicopathologic characteristics as right-sided MSI-H CRCs. We did not find any significant clinicopathological difference between HNPCCs and sporadic MSI-H CRCs.