Interactions of familial and hormonal risk factors for large bowel cancer in women

Background Family history of colorectal cancer has been consistently associ ated with an increased personal risk of this disease. Since evidence sugges ts that hormones are related to colon cancer risk in women, the effect of f amily history on large bowel incidence may be modified according to endogen ous and exogenous hormone levels. Methods We analysed data from a population-based case-control study of fema le colorectal cancer to evaluate family history and cancer risk. Cases (n = 702) were female residents of Wisconsin with a new diagnosis of colorectal cancer, identified through a statewide tumour registry. Controls (n = 2274 ) were randomly selected from lists of licensed drivers and from rosters of Medicare beneficiaries. All relative risks (RR) were adjusted for age, bod y mass index, smoking and alcohol history, education, and use of hormone re placement therapy. Results Compared with women who reported no history of cancer in a first de gree relative, women with a family history had an RR of 2.07 (95% confidenc e interval [CI] : 1.60-2.68). Regardless of which parent was affected, risk s were increased about twofold, while sibling history was associated with a bout a 50% increase in risk. Risk was greater if more than one family membe r was affected (RR 3.65, 95% CI: 1.81-7.37). The association between family history and risk was stronger for colon cancer than for rectal cancer. The re were no indications that exogenous hormonal factors, notably hormone rep lacement use, modified these risks. There was a suggestion that high parity attenuated the risks associated with family history (P = 0.07). Conclusions These results confirm that family history of colorectal cancer is associated with a doubling of risk for large bowel cancer in women; some histories were associated with greater risk. This relation was not substan tially different among subgroups of women with varying exogenous and endoge nous hormone exposures.