Objective: To determine characteristics of hereditary nonpolyposis colorectal cancer (HNPCC) and the implications for screening and treatment.
Design: Longitudinal.
Setting: Nationwide.
Method: Genealogic studies were performed in 114 families referred to the Netherlands Foundation for Detection of Hereditary Tumours because of a suspected inherited form of colorectal cancer.
Results: Forty-one families met the criteria for HNPCC: These families included 194 patients with colorectal cancer (84 females and 110 males). The mean age at diagnosis was 44 years (range: 16-74). In 92% the tumour was diagnosed before the age of 60 years. Fifty-eight per cent were located in the proximal colon. Twenty-three per cent of the patients had multiple primary colorectal cancer. The cumulative risk of developing a second colorectal cancer was 23% after 10 years of follow up. Cancer of the endometrium, stomach and urinary tract were the most frequent extracolonic cancers.
Conclusions: Periodic examination of first-degree relatives of patients from HNPCC families should start between the ages of 20 and 25 years. The recommended interval between consecutive examinations is 2-3 years. After the age of 60 years screening may be performed at a lower frequency. The right colon in particular should be investigated. A subtotal colectomy is indicated at the time of diagnosis of the initial colon cancer, because of the risk of multiple primary tumours.