title: Familial risk of small intestinal carcinoid and adenocarcinoma.
abstract: OBJECTIVE
  Small intestinal cancer (SIC) is rare, and its etiology is poorly understood. We compared clusters of families with SICs of different histologic subtypes.
  
  
  METHODS
  By using the nationwide family cancer data sets of Sweden and Finland, we identified a cohort of 9964 first-degree relatives of 1799 patients with SIC, diagnosed from 1961 through 2009. Data were collected from time periods as long as 47 years (mean, 35.4 y), and cancer incidence was determined. Standardized incidence ratios (SIRs) were calculated and stratified by sex, age, time period, and cancer type, using the incidence rates for the entire national population as the reference.
  
  
  RESULTS
  Among the 1799 SIC cases, 1.1% had a sibling with SIC, so the SIR was 11.8 (95% confidence interval [CI], 7.2-18.2); 1.1% had a parent or child with SIC (SIR, 3.5; 95% CI, 2.0-5.6). The SIR of concordant carcinoid histology of SIC among siblings was 28.4 (95% CI, 14.7-49.6; n = 12) and in parent-child pairs was 9.9 (95% CI, 5.4-16.6; n = 14). The familial risk of concordant histologic subtypes increased for siblings diagnosed with adenocarcinoma, but only 2 familial cases were identified. In family members of patients with SIC of the adenocarcinoma subtype, risks of colorectal and bladder cancer were modestly but significantly increased compared with the general population. Family members of patients with SIC of the carcinoid subtype had an increased risk for kidney cancer and polycythemia vera.
  
  
  CONCLUSIONS
  Based on data from our population-based study, first-degree relatives of patients with small intestinal carcinoid tumors have developed these tumors with high incidence. Because of the rareness of this tumor, the absolute risk remains moderate even within families. Gastroenterologists could inform patients with small intestinal carcinoids about the familial risk and encourage counseling for their first-degree relatives. Studies are needed to identify genetic factors that affect susceptibility to SIC.
authors.affiliation: Division of Molecular Genetic Epidemiology, German Cancer Research Center, Heidelberg, Germany. e.kharazmi@dkfz.de
authors.forename: Elham
authors.initials: E
authors.lastname: Kharazmi
authors.forename: Eero
authors.initials: E
authors.lastname: Pukkala
authors.forename: Kristina
authors.initials: K
authors.lastname: Sundquist
authors.forename: Kari
authors.initials: K
authors.lastname: Hemminki
mesh_terms: D000230:Adenocarcinoma / Q000453:epidemiology*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002276:Carcinoid Tumor / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005387:Finland / Q000453:epidemiology; D030342:Genetic Diseases, Inborn / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D007414:Intestinal Neoplasms / Q000453:epidemiology*; D007421:Intestine, Small / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D018570:Risk Assessment; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: CI; FAP; Genetics; HNPCC; Inherited; MEN1; Pathogenesis; Risk Factor; SIC; SIRs; confidence interval; familial adenomatous polyposis; hereditary nonpolyposis colorectal cancer; multiple endocrine neoplasia 1; small intestinal cancer; standardized incidence ratios