Objective: The aim of this study was to identify published studies quantifying familial colorectal cancer (CRC) risks in first-degree relatives of CRC and colorectal adenoma (CRA) cases and, through a meta-analysis, obtain more precise estimates of familial risk according to the nature of the family history and type of neoplasm.
Methods: Twenty-seven case-control and cohort studies were identified, which reported risks of CRC in relatives of CRC cases and nine, which reported the risk of CRC in relatives of CRA cases. Pooled estimates of risk for various categories of family history were obtained by calculating the weighted average of the log relative risk estimates from studies.
Results: The pooled estimates of relative risk were as follows: a first-degree relative with CRC 2.25 (95% CI = 2.00-2.53), colon 2.42 (95% CI = 2.20-2.65), and rectal 1.89 (95% CI = 1.62-2.21) cancer; parent with CRC 2.26 (95% CI = 1.87-2.72); sibling with CRC 2.57 (95% CI = 2.19-3.02); more than one relative with CRC 4.25 (95% CI = 3.01-6.08); relative diagnosed with CRC before age 45, 3.87 (95% CI = 2.40-6.22); and a relative with CRA 1.99 (95% CI = 1.55-2.55).
Conclusions: Individuals with a family history of CRC and CRA have a significantly elevated risk of developing CRC compared with those without such a history. Risks are greatest for relatives of patients diagnosed young, those with two or more affected relatives, and relatives of patients with colonic cancers.