According to the latest statistics from the Hong Kong Cancer Registry, colorectal cancer (also called large bowel cancer) is the commonest cancer with more than 4,900 new patients diagnosed in the year 2014 and more than 2,000 persons died from this condition making it the second most lethal cancer locally1. Moreover, there has been a steadily increasing trend in the number of new cases in the territory over the past few decades (Table 1). We have previously shown that Hong Kong has an exceptionally high incidence of colorectal cancer in the young population2.
While environmental and lifestyle factors play a major role in the cause of most colorectal cancers (for which affected individuals are usually in their 60s and 70s), about 5-10% of all colorectal cancers is associated with heredity, that is, these individuals suffer from colorectal cancer due to defects in their genes3-4.
The two main types of hereditary colorectal cancers are Familial Adenomatous Polyposis (FAP) and Lynch Syndrome (LS; also called Hereditary Non-Polyposis Colorectal Cancer, HNPCC). They are caused by germline mutation of the Adenomatous Polyposis Coli (APC) and Mismatch Repair (MMR) genes, respectively. Both these conditions are inherited in an autosomal dominant fashion, that is, offspring of an affected individual will have 50% chance of inheriting the condition and predispose to colorectal and other related cancers. Moreover, affected individuals tend to develop these cancers early in their life. The psychological and economic burdens on these families are profound.
For high-risk individuals from hereditary colorectal cancer families, pre-symptomatic detection and treatment of precancerous adenoma or early cancer by regular checkup (called surveillance) is the most effective way to prevent colorectal cancer and its associated morbidity and mortality5-9. In the past two decades, advances in molecular genetic technology have allowed detection of these abnormal genes causing the various types of hereditary colorectal cancer syndromes. Genetic diagnosis and screening make it possible to distinguish accurately the disease-gene carriers from those who have not inherited the defective gene within an affected family, thus allowing an accurate risk assessment of all the at-risk family members. The non-carriers will be relieved from the psychological burden as well as the chore of continuous surveillance. Resources can then be concentrated on counseling and vigilant surveillance of those carrying the defective gene to prevent cancer development.
Management of these hereditary colorectal cancer families requires a multidisciplinary approach and is best organized by a dedicated registry10. Since its establishment in 1995, the Hereditary Gastrointestinal Cancer Registry has developed a comprehensive service for these hereditary colorectal cancer families in Hong Kong10. As of May 2017, the Registry has recruited 987 families with 634 index patients and 1,740 at-risk relatives being alive.