REPRODUCTIVE FACTORS AND RISK OF BRAIN, COLON, AND OTHER MALIGNANCIESIN IOWA (UNITED-STATES)

The influence of parity on the risk of cancers of the female breast an d reproductive organs is well established. However, non-reproductive s ites have received less attention. Mail questionnaire data gathered fr om incident female cases (169 brain; 332 colon; 260 rectal; 145 kidney ; and 169 pancreas cancers), and 821 population-based controls in Iowa (United States) were used to measure the effect of parity and age at first birth on risk of these malignancies. Relative to nulliparous wom en, ever-parous women were at significantly decreased risk of brain ca ncer (odds ratio [OR] = 0.44, 95 percent confidence interval [CI] = 0. 3-0.7) and of colon cancer (OR = 0.67, CI = 0.5-0.97), after adjustmen t for age and other risk factors. The OR for the other sites did not d iffer significantly from 1.0. The lower risk of brain cancer among par ous women was similar in younger and older age groups, in patients dia gnosed with glioblastoma and astrocytoma, and among ever- and never-sm okers. The findings for colon cancer are consistent with observations from other studies. In the context of limited laboratory and clinical evidence implicating hormones in brain neoplasia, these findings may s uggest a role for hormonal factors in brain cancer etiology. Hormonal factors deserve more detailed future consideration as risk factors in brain cancer.