Mismatch Repair Protein Expressions in Cohort of Colorectal Carcinoma Patients in Lagos

Colorectal carcinoma (CRC) is a major cause of morbidity and mortality worldwide. Microsatellite instability pathway is important in the pathogenesis of CRC. Immunohistochemistry expression of mismatch repair (MMR) proteins serves as surrogate marker for MMR gene mutation.

This study aimed to determine MSI status of a cohort of CRC cases using immunohistochemistry.

Surgical pathology blocks of resected colonic carcinoma (CC) between 2011 and 2015 were extracted from our departmental archives and The Specialist Laboratories in Lagos. Immunohistochemical expression profile of 4 MMR proteins was assessed in the representative blocks and this was correlated with the demographic and pathological characteristics.

There were 19 males and 16 females with CC, mean age of 51.6 years, and 40% of them were below 50 years of age. Twenty (57.1%) out of the 35 CC cases seen were mismatch repair proficient (pMMR) while the remaining 15 (42.9%) were mismatch repair deficient (dMMR). Seven dMMR cases were seen equally on the right and left colonic tumors respectively. Five (71.4%) out of the 7 mucinous tumors in this study were dMMR, right sided with 3 of them in patients who were below 50 years of age.

The frequency of mismatch repair deficiency in CC among Nigerians is high, and presence of right-sided mucinous colon cancer in patients below 50 years is highly suggestive of dMMR status. Mutation studies of larger patient samples to determine the percentage with germline mutation will further our knowledge, and influence therapeutic options for CC.