Hereditary gastrointestinal cancer
Hereditary gastrointestinal cancer genetic testing is used to identify germline pathogenic variants that predispose to cancers of the colorectum, stomach, and pancreas. The leading syndromes are , the most common hereditary colorectal cancer predisposition, and , alongside hereditary diffuse gastric cancer, , , and . Most are inherited in an autosomal dominant manner, whereas is autosomal recessive, and more than a dozen causative genes are implicated across these sites. Lynch syndrome arises from pathogenic variants in the mismatch-repair genes MLH1, MSH2, MSH6, or PMS2, or from EPCAM deletions that silence MSH2. Biallelic variants in the mismatch-repair genes cause constitutional MMR deficiency (CMMRD), a rare childhood cancer predisposition syndrome. Affected individuals often have CRC or cancer of the small intestine prior to the second decade of life. The cutaneous phenotype in affected individuals may be remarkably similar to that seen in , as nearly all will have café au lait macules. A precise molecular diagnosis secures the syndrome, defines organ-specific cancer risk, and directs surveillance and cascade testing of at-risk relatives, as set out in international management guidelines.
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