Colorectal or colon Cancer is often described as a “lifestyle disease”, commonly linked to diet, obesity, aging, and lack of physical activity. However, doctors warn that for some people, the risk begins long before lifestyle factors play a role—within their genetic inheritance.
A small but important proportion of colorectal cancers are caused by inherited gene mutations passed down through families. These conditions are known as hereditary colorectal cancer syndromes, and identifying them early can provide a powerful opportunity for prevention, early detection, and family-wide risk reduction.
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Hereditary colorectal cancers usually follow an autosomal dominant inheritance pattern, meaning the genetic risk can pass from one generation to the next. “The most hereditary colorectal cancer syndromes follow an autosomal dominant pattern (meaning risk can pass from one generation to the next), though a few are autosomal recessive (risk rises when a person inherits altered copies from both parents).” Dr. Thangarajan Rajkumar, Director of Research (Oncology), MedGenome Labs Ltd., told Times Now Health.
According to Dr. Rajkumar, two of the most well-known hereditary syndromes include:
A common misunderstanding is that hereditary colorectal cancer affects only the colon. In reality, Lynch syndrome is linked to several other cancers, including:
Lynch syndrome accounts for around 3 to 5 percent of colorectal cancer cases
Lynch syndrome occurs due to inherited defects in the DNA mismatch repair system, which normally corrects mistakes during cell division. When this repair system fails, tumours often develop a distinctive feature called Microsatellite Instability, which doctors can detect through specialized testing.
Meanwhile, familial adenomatous polyposis (FAP) is caused by mutations in the APC Gene. People with FAP develop hundreds to thousands of colon polyps, often beginning in adolescence. According to Dr. Rajkumar, without treatment, the lifetime risk of colorectal cancer can approach 100 per cent by mid-adulthood. “The mutation carriers can have an almost 100 per cent risk of colorectal cancer by around mid-adulthood if not managed. FAP can also be associated with certain other tumours (some with malignant potential), which is why families need structured follow-up rather than one-off tests,” he said.
Doctors rely heavily on family history to identify people who may need genetic evaluation. A few warning signs include:
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