Introduction

Colorectal cancer is a common disease of Western populations. In the Netherlands (population: 15 million), 8000 new cases were diagnosed in 1996. In 5–10% of all colorectal cancer cases, genetic factors play a significant role. Two main groups of the hereditary form of colorectal cancer are commonly distinguished: polyposis types with multiple colorectal polyps, and non-polyposis types without multiple polyps. Non-polyposis colorectal cancer can be sub-classified into hereditary non-polyposis colorectal cancer (HNPCC), characterized by early-onset colorectal cancer and endometrial cancer, and families with clustering of colorectal cancer at an advanced age. Within the polyposis types, a further distinction is made between adenomatous, hamartomatous and hyperplastic polyposis, and polyposis with mixed pathology (Vasen, 2000).

During the last decade, great progress has been made in molecular genetics. The genes responsible for most of the inherited forms of colorectal cancer have been identified, and DNA testing has been implemented in clinical practice on a large scale. The identification of people at high risk of cancer is important as preventive measures may be taken in such cases, which may lead to a reduction in the cancer-related mortality.

Decisions on the protocol of surveillance recommended in the various forms of heredirary cancers are made on the basis of the level of risk of developing a specific cancer and the availability of sensitive and specific screening tests.