Carcinoid tumors in Denmark 1978–1989 and the risk of subsequent cancers. A population‐based study

Background. Previous studies have suggested an excess cancer risk in patients with carcinoid tumors. This association was reexamined using truly population‐based data. Methods. By means of data from the Danish Cancer Registry all carcinoid tumors diagnosed in Denmark between 1978 and 1989 were identified. All patients with primary carcinoid tumors were studied for the occurrence of subsequent cancers. The numbers of subsequent cancers observed in the follow‐up period were compared with the expected numbers calculated from population rates. Results. A total of 1029 patients with carcinoid tumors were identified (464 men and 565 women). The annual age‐adjusted incidence rates (world standardized) for carcinoid tumors during 1978–1989 were stable at about 1.1 per 100,000 person‐years for both men and women. The patients were followed for the occurrence of subsequent cancers over a period comprising 2512 person‐years. Thirty subsequent cancers were identified in 29 patients. The overall relative risk of subsequent cancers was 1.1 (95% CI, 0.8–1.6). Subsequent cancers of the thyroid were in excess (RR, 21.4; 95% CI, 2.4–77.1; n = 2), as were tumors of the brain and nervous system (RR, 5.4; 95% CI, 1.1–15.9; n = 3) and non‐Hodgkin's lymphomas (RR, 5.8; 95% CI, 1.2–16.9; n = 3). Conclusions. Overall, this population‐based study does not support previous studies of an excess cancer risk in patients with carcinoid tumors. Increased risks of cancers of the thyroid, tumors of the brain and nervous system, and non‐Hodgkin's lymphomas were observed, but these findings were based on few cases.