Colorectal cancer in South Africa: a heritable cause suspected in many young black patients.

BACKGROUND: Colorectal carcinoma (CRC) has a low incidence among the black African population. Largely unrecognised in the scientific literature is the fact that a disproportionately large number of young black patients (<50 years old) present with CRC.
OBJECTIVES: To analyse those tumours, which we propose may link them to morphological features associated with known genetic pathways.
METHODS: A retrospective review of South African patients histologically diagnosed as having CRC by the Division of Anatomical Pathology, National Health Laboratory Service (NHLS) and the University of the Witwatersrand (1732 patients from 1990 to 2003). The histology was fully reviewed in 609 patients (1997-2002), and all specimens from patients <50 years of age were subjected to immunohistochemistry tests for mismatch repair proteins, as well as APC and p53 proteins.
RESULTS: Most young patients (<50 years) were black (41% v. 10% white; p < or = 0.001). Blacks had predominantly proximal tumours and significantly more poorly differentiated and/or mucinous tumours (p = 0.006), and loss of mismatch repair protein expression was more evident than in whites.
CONCLUSIONS: It seems likely that CRC in young blacks develops through the accumulation of mutations, most probably via mismatch repair deficiency or promoter methylation, which in turn is linked to poor differentiation and a mucinous architecture.