MICROSATELLITE INSTABILITY IN AND PATHOLOGICAL CHARACTERISTICS OF COLORECTAL CARCINOMAS IN OAUTHC, ILE-IFE, WESTERN NIGERIA

Abstract

Background; Colorectal carcinoma (CRC), the commonest malignancy of the gastrointestinal
tract, appears to occur within two epidemiological contexts: a high incidence , and a low

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incidence one. Colorectal carcinomas in Africa fall into the low-incidence sub-group and seems
to have distinct clinicopathological features and, it is emerging, may also have different molecular
characteristics underlying their aetiopathogenesis. Whereas the aetiological associations and
molecular pathways of causation of high incidence CRC have been extensively studied, the low
incidence CRCs are yet to be studied in nearly as much detail. In this study, we examined
Microsatellite instability, one of the putative molecular pathways of CRC pathogenesis, and
related our findings with the clinicopathological characteristics of 55 cases on our accession
records.
Methodology; We retrospectively studied these for site of the lesion in each case, gross growth
patterns of the tumour, the histological type and stage of disease as well as and other incidental
pathological changes in adjoining mucosa. To detect microsatellite instability,
immunohistochemical stains for DNA mismatch proteins; MLH1 and MSH2 were done.
Results; The mean age for our cohort of cases was 49.2 years more than half was found in
patients younger than 50 years, and the site of CRCs was the caecum (24%); The exophytic
growth pattern was the commonest and adenocarcinoma was the commonest histological type
but mucinous carcinomas made up 33% of them. Microsatellite instability was found in 35% of
our cases. The MSI-positive tumours were commoner in patients younger than 50 years and
were more proximally located and with an exophytic growth pattern. Half of the mucinous
carcinomas showed microsatellite instability. This was statistically significant.
Conclusion; Compared to studies from the USA, Europe and Australia, where the high
incidence CRC is prevalent, Microsatellite Instability was found in a higher number of the
colorectal carcinomas in this study. On the face of it, this suggests that MSI may be a more
plausible putative pathogenetic pathway for low-incidence CRCs, which our cases typify.
Obviously, our findings need to be validated using direct molecular testing. If further validated
in larger multicentre studies, these findings have implications for the understanding of the
aetiology, prognosis and treatment of low-incidence CRCs.