The Melbourne Colorectal Cancer Study. Characterization of patients with a family history of colorectal cancer.

The characteristics of 702 colorectal cancer patients are described in relation to the presence of absence of a family history of colorectal cancer in near relatives. No statistically significant associations were found between those with a family history of colorectal cancer and age at detection, sex, country of birth, religion, number of cancers (single, synchronous, or metachronous), previously removed benign colorectal polyps, and adenomatous polyps found in the resection specimen. The family history rate of colorectal cancer for colon cancer cases was statistically significantly higher than for rectal cancer cases (chi 2(1) = 3.8, P = .05) and there was a gradient of decreasing risk from colon to rectum. The family history rate of colorectal cancer in parents of those who were less than 50 years old was twice that of those 50 or older (P = .07), consistent with the view that earlier age of onset is a characteristic of those with a family history of colorectal cancer. There was a statistically significantly higher family history rate of colorectal cancer in respondents who knew of the disease compared with those who did not (chi 2(1) = 5.5, P less than .05). It is unclear if this effect represents recall bias or self-selection bias. In contrast, the rates for a family history of heart disease and stroke were similar, irrespective of the respondent's knowledge of their colorectal cancer status. Thus in the Melbourne study, the family history rate of colorectal cancer was higher in colon cancer than in rectal cancer, there was a decreasing gradient of risk from colon to rectum, and a tendency for earlier age of onset of colorectal cancer in those with a history of this cancer in a parent.