COLORECTAL CARCINOMAS IN NATIONAL HOSPITAL ABUJA, NIGERIA (SURGICAL PATHOLOGY AND MMR PROTEIN EXPRESSION, 2004-2013)

Abstract

Study Background, Aim and Objective: Tumours with microsatellite instability occur more frequently in younger patients, are more frequently located proximal to the splenic flexure and exhibit exophytic growth, poor differentiation, extracellular mucin production, and a Crohn’s-like lymphocytic reaction. Cell lines from tumours with microsatellite instability are less sensitive to alkylating agents. Such tumours have a better survival rate relative to microsatellite-stable (MSS) tumours of similar stage. The aim of this study is to do a pathological review and to determine the characteristics and frequency of microsatellite instability status in a series of colorectal cancers in Abuja, Nigeria with a view to suggesting possible aetiological factors. Method: The study is a retrospective histopathological and immunohistochemical study of 175 paraffin tissue blocks with histologically proven colorectal carcinoma and available clinical information spanning a 10 year period. Results The mean age was 50.8 years (range 21-94 years) with a near-equal gender distribution (M: F ratio-1.08:1). The vast majority of patients (69.8%) were aged between 40 and 69years with 21.6% patients below age 40years. Well differentiated carcinomas were the commonest, accounting for 81 or 43.6%. Tumours of poorer grade were relatively more common in the younger age groups. The left sided colonic tumours were more commonly endophytic/annular, the right colonic tumours were more commonly exophytic/fungating (p value = 0.02). Overall, 140 out of 175samples were tested for microsatellite instability (MSI) using standard IHC, 45 patients (32.1%) had high frequency MSI (MSI-H) tumours and 75 patients (53.6%) had microsatellite stable (MSS) tumours. A right sided location and poor differentiation correlated with MSI-H tumours (p values of 0.013 and <0.001 respectively). The strongest associations were found between MSI-H status and residual adenomatous tissue, worse tumour grade, more Crohn-like feature and more advanced pathological staging with p values <0.001 each. Conclusions: High frequency MSI (MSI-H) colorectal carcinomas were relatively more frequent in our study (32.1%). The disease occurs at a much younger age group than in Caucasians and Arabs. Premalignant (adenomatous) lesions are few accounting for the low colon cancer rates in our study. The CIMP pathway is suggested to play a greater role than is currently ascribed to it in the tumorigenesis. The rarity of adenomatous polyps also suggests the possibility of other precursors like inflammation

COLORECTAL CARCINOMAS IN NATIONAL HOSPITAL ABUJA, NIGERIA (SURGICAL PATHOLOGY AND MMR PROTEIN EXPRESSION, 2004-2013)