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Hereditary Colorectal Cancers Syndromes

Colorectal cancer (CRC) is the leading cancer in Singapore and despite recent advances in treatment, the prognosis for CRC patients with advanced stage disease is poor. There is a need to identify individuals with an increased CRC risk so that screening can commence.

First degree relatives of CRC have an approximately twofold increased risk of developing the disease themselves, and the risk increases with increasing number of affected family members and if CRC is diagnosed at a young age. This association may be due to various factors such as shared environment, inherited genetic mutations, or a combination of both.

Hereditary colorectal cancers such as Familial Adenomatous polyposis (FAP) syndromes and Lynch Syndrome are two inherited CRC that account for 5% of all CRC. In these syndromes, the development of CRC is very high. In Lynch Syndrome, patients are also at risk of developing other cancers such as endometrial, small bowel, gastric and urothelial (urinary system) cancers. If a family member is confirmed to have the diagnosis, persons at risk of developing are advised to start colonoscopy screening early. For example, Lynch syndrome patients are advised to start colonoscopy screening every 1-2 years beginning at age 20-25 years. For FAP, routine endoscopic surveillance has been advised to commence from 10 years old and colon surgery may be required once the patient reaches the age of 15-25 years old.

The Singapore Polyposis Registry (SPR) was established in 1989 in Singapore General Hospital. Aim of this initiative is to provide a central registry service to all doctors in Singapore to facilitate identification, surveillance and management of families and individuals at high risk of getting colorectal cancer. Various research projects performed using data from the SPR have also resulted in important genetic testing and identification of at risk individuals. This has led to important data improving diagnosis, survival and genetic counselling for patients.

The High Risk Clinic service is closely linked to the services provided by the SPR. The aim is to improve the prognosis of disease through identification of high-risk families, who would benefit from screening, construction of family trees, leading to early diagnosis of affected individuals and subsequent cancer prophylactic treatment. The High Risk Clinic service is also currently supported by department molecular biology, cell-kinetic and anorectal physiology laboratories. Patients are thus ensured accurate pre or post clinical diagnosis, genetic testing and detailed post–surgical functional assessments for those who undergo operations. There are also additional aims to co-ordinate surveillance and information for the patients, provide education and knowledge to the patients and family members, continue to perform local research and participate in international collaborations to understand the diseases better.

In the High Risk Clinic, the patients will have a thorough discussion with the genetic counsellor and physician with regards to a detailed clinical and family history. If it is ascertained that the individual is at risk of a hereditary colorectal cancer, genetic testing may be advised. In current testing procedures, blood may be collected and analysed either locally or in an overseas laboratory depending on the type of test. The interpretation of the results will once again be performed by the genetic counsellor and physician. The necessary screening procedures will be subsequently recommended.