Incidence trends and risk factors of carcinoid tumors: a nationwide epidemiologic study from Sweden

Carcinoids are rare indolent neuroendocrine tumors, mainly located in bowel, stomach, and lung. Their etiology is virtually unknown although a family history is a minor cause. Site specific incidence trends and several risk factors of carcinoid tumors were studied based on the nationwide Swedish Family-Cancer Database of 10.2 million individuals and their more than 1 million tumors. Data on a total of 5184 carcinoid tumors were retrieved from the Cancer Registry covering years 1958-1998. The overall age-adjusted incidence rates were 2.0 for men and 2.4/100,000 for women in 1983-1998. Appendix was the main site for women whereas small intestine was the main site for men. The incidence of all carcinoids, including those at the main sites increased during the follow-up period but appeared to plateau in the middle of the 1980s. Appendiceal carcinoids showed an unusually early onset with a maximum incidence at age 15-19 years for women and 20-29 years for men. Among women, parity was not related to the age specific incidence of carcinoid tumors. A Poisson regression analysis showed that family history of carcinoids in first-degree relatives (relative risk, 3.6), well educated social background (relative risk for professionals, 2.8), and birth in large cities were risk factors. The data suggest that the increase in carcinoid tumors may be largely ascribed to the application of advanced medical viewing techniques that detect asymptomatic tumors. However, the difference in incidence between men and women in appendiceal tumor may be real and independent of parity.