Familial risk of colon and rectal cancer in Iceland: evidence for different etiologic factors?

• Published in: International Journal of Cancer
• Main Authors: Stefansson, T, Moller, P, Sigurdsson, F, Steingrimsson, E, Eldon, B
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Iceland
• Online Access: https://doi.org/10.1002/ijc.21835; https://ora.ox.ac.uk/objects/uuid:1a8ce5fb-90f2-458a-ba43-8c19a6676386

The aim of this study was to characterize the familial risk of colon and rectal cancer using 2 population-based registries in Iceland, the Icelandic Cancer Registry and a genealogy database. The standardized incidence ratio (SIR) was used to estimate the risk among relatives of colorectal cancer index cases diagnosed in Iceland over a 46-year period (1955-2000). The 2,770 colorectal cancer patients had 23,272 first-degree relatives. Among first-degree relatives, there was an increased risk of both colon (SIR 1.47, 95% confidence interval (CI) 1.34-1.62) and rectal cancer (SIR 1.24, 95% CI 1.04-1.47). An increased risk of colon cancer was observed among siblings of colon cancer patients (SIR 2.03, 95% CI 1.76-2.33), whereas no such increase was observed for parents or offspring. Furthermore, the risk of rectal cancer was only increased among brothers (SIR 2.46 95% CI 1.46-3.89) of rectal cancer patients and not among their sisters (SIR 1.0 95% CI 0.40-2.06). The added risk of colon cancer among first-degree relatives was independent of site of colon cancer in the proband. Our results confirm that family history of colorectal cancer is a risk factor for the disease. However, family history has a different association with colon cancer than with rectal cancer, suggesting that the 2 cancer types may have different etiologic factors. Our results have implications for colon and rectal cancer screening programs.