| Summary: | Colorectal cancer (CRC) is the third most common cancer in men and the second in women worldwide. Approximately 3% to 5% of colorectal cancers are attributable to a hereditary cancer predisposition related to DNA mismatch repair (MMR) deficiency. Deficient MMR (dMMR) results in an inability to correct DNA replication errors and therefore results in an increased risk of cancer. Individuals with LS have hereditary (germline) defects in one of their genes that encode for an MMR protein. This predisposes them to colorectal and other types of cancer. LS is the most common familial CRC syndrome. The gold standard for detection of a germline mutation in MMR genes (MMR deficiency) is germline genetic testing by sequencing and deletion-duplication analysis. However, as mutations in one of four MMR genes can underlie LS, and because of the time-consuming nature and considerable economic burden associated with sequencing all four MMR genes, the decision to offer germline genetic testing to diagnose LS is commonly made in a stepwise manner. Patients may be pre-screened for potential hereditary CRC based on age or family history, followed by testing of tumour samples for signs of dMMR, and ultimately germline genetic testing. To assist decision-makers considering the implementation of dMMR tumour testing, CADTH conducted a health technology assessment (HTA) on the clinical utility, diagnostic accuracy, cost-effectiveness, and related patient perspectives and experiences of dMMR testing strategies. The ability of dMMR tumour test results to inform CRC prognosis or chemotherapy response was also evaluated
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