Family history and risk of colorectal cancer in the multiethnic population of Hawaii.

Increased risk of colorectal cancer in individuals with family history of the disease has been observed consistently in past studies. However, limited attention has been given to the influence of ethnicity, the characteristics of the proband's tumor, and kinship. A population-based case-control study was conducted between 1987 and 1991 in Hawaii among 1,192 incident colorectal cancer cases and 1,192 sex-, age-, and ethnicity-matched population controls. The study identified 7,673 relatives for the cases and 7,823 relatives for the controls. With an estimating equation-based regression method, relatives of cases were found to have a 2.5-fold increased risk of colorectal cancer compared with relatives of controls (95% confidence interval (CI) 1.8-3.4) after adjustment for covariates. This increase in risk was greater for Japanese (odds ratio (OR) = 3.0, 95% CI 1.7-5.4) than Caucasians (OR = 1.8, 95% CI 1.2-2.9), for siblings (OR = 3.1, 95% CI 2.1-4.6) than parents (OR = 2.0, 95% CI 1.1-3.1), and when the index patient was diagnosed before the age of 55 years (OR = 4.1, 95% CI 2.1-8.0) with multiple tumors (OR = 9.5, 95% CI 4.4-20.6), with a distant stage (OR = 4.6, 95% CI 2.7-7.8), or with cancer of the right colon (OR = 3.0, 95% CI 2.0-4.4) or the rectum (OR = 3.0, 95% CI 1.8-4.8). The increase in risk was not affected by the relative's sex. Relatives of cases were not at increased risk for other common cancers. It is estimated that approximately 11.1% and 6.5% of colorectal cancers are attributable to a first degree family history of the disease for Japanese and Caucasians, respectively. These data and those of previous studies strongly suggest that individuals with a family history of colorectal cancer in a first degree relative are at increased risk for the disease and should receive regular diagnostic screening. Characteristics of the index case, such as age and stage at diagnosis, subsite and number of tumors, and race, as well as kinship, may be important in assessing the colorectal cancer risk of a relative.