Approximately 150,000 Americans are affected by colorectal cancer each year as well as 500,000 worldwide. Much of the morbidity and mortality of the disease could be prevented if we understood more about the risk of the cancer developing and were able to intervene with appropriate treatment.
3-4% of colorectal cancer cases are inherited as a familial syndrome. The most common of these is Lynch syndrome, which is also know as hereditary nonpolyposis colorectal cancer. It is caused by a mutation in one of four mismatched genes. The identification of such patients is important, but it is impractical to screen every patient for these mutations because current tests cost around $3,000. Clinical algorithms have therefore evolved to estimate risk of developing Lynch Syndrome.
Some Scottish researchers recently reported on a new algorithm to identify patients who present with one of the 4 mismatched genes. They used a population based approach in newly diagnosed patients under 55 years and used clinical features to develop a better predictive model to estimate which patients with the disease was a likely mutation carrier.
Genetic testing can then be performed on a smaller pool of likely patients. They published the algorithm on a website for anyone who is interested (link).
Hereditary cancers occur in several tumour types, including ovarian, breast and colorectal cancers. Lynch Syndrome is probably the most prevalent, occurring in 1 or 2 per 1,000 people, so the syndrome is neither common nor rare. It is important to identify it early because it is grows from a benign tumour to a carcinoma (cancer) much more quickly than sporadic colorectal cancer in the general population. Fortunately, there are clear markers for the syndrome that are not present in the other hereditary cancers.
The findings of the Scottish research suggest, for example, that there should be around 3300 to 6000 carriers of detectable mutations in the genes of patients with newly diagnosed colorectal cancer in the US and similarly for Europe. Each carrier has a family; the job of the medical profession is now to find them. There is a demonstrated survival benefit in patients with Lynch Syndrome under surveillance than not, so tracking down the patients and their families of carriers will affect many future generations.
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