Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Ontario, Canada.
AIMS: MYH is a DNA glycosylase in the base excision repair pathway. Germ-line biallelic mutations in the MYH gene are associated with the development of multiple colorectal adenomas and colorectal carcinoma (CRC). A slightly increased risk of CRC is suggested in monoallelic MYH mutation carriers. The aim was to characterize the histopathological features of carcinomas from biallelics and monoallelics. METHODS AND RESULTS: Clinicopathological features of 57 colorectal carcinomas from 50 patients identified in familial CRC registries were recorded. These included 16 cancers from 14 MYH biallelics; 25 cancers from 22 MYH monoallelics; and 16 cancers from 14 controls. Carcinomas in biallelics demonstrated tubular, papillary or cribriform patterns as the predominant histological subtype, and main histological groups differed according to mutation status (P = 0.0053). All biallelic cancers were low grade, with high-grade tumours more common in monoallelics and controls (P = 0.002). Synchronous polyps were observed in 75% of biallelics, 33% of monoallelics and 43% of controls (P = 0.035). Serrated carcinoma was the predominant type in 12% (3/25) of the monoallelics but in none of the biallelics or controls. MYH immunohistochemistry failed to distinguish between groups. CONCLUSIONS: Neither pathological features nor immunohistochemistry could predict the MYH mutation status of CRCs in this study.