Reproductive factors and colon cancer: the influences of age, tumor site, and family history on risk (Utah, United States).

The Utah (United States) Population Database was used to evaluate the associations between reproductive factors and colon cancer risk and the impact that family history, age at diagnosis, and tumor site have on these associations. From the cohort of (White) women in the database, all first-primary cases of colon cancer (n = 819) and controls who had complete fertility information (n = 3,202) were examined. The majority of tumors (68.6 percent) among women diagnosed at age 64 years or less were in the distal segment of the colon, while among women 65 or older, the majority of tumors (55.7 percent) were proximal. Women diagnosed before age 65 had a lower risk of colon cancer with increasing numbers of liveborn children (odds ratio [OR] = 0.6, 95 percent confidence interval [CI] = 0.3-0.9 for women with five or more children compared with women with one or two children). A long interval between first and second births (first birth-interval) was associated with increased risk of tumors in the distal segment of the colon (OR = 1.4, CI = 1.0-2.0) and among women diagnosed before age 65 (OR = 1.6, CI = 1.0-2.5); a longer, average birth-interval was associated with increased risk of proximal tumors (OR = 1.5, CI = 1.1-2.1).(ABSTRACT TRUNCATED AT 250 WORDS)