| Abstract: | The influence of parity on the risk of cancers of the female breast and reproductive organs is well established. However, non-reproductive sites have received less attention. Mail questionnaire data gathered from incident female cases (169 brain; 332 colon; 260 rectal; 145 kidney; and 169 pancreas cancers), and 821 populationbased 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 women, ever-parous women were at significantly decreased risk of brain cancer (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 adjustment for age and other risk factors. The OR for the other sites did not differ significantly from 1.0. The lower risk of brain cancer among parous women was similar in younger and older age groups, in patients diagnosed with glioblastoma and astrocytoma, and among ever- and never-smokers. 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 suggest a role for hormonal factors in brain cancer etiology. Hormonal factors deserve more detailed future consideration as risk factors in brain cancer.Dr Cantor is with the Environmental Epidemiology Branch, National Cancer Institute, Bethesda, MD, USA. Dr Lynch and Ms Johnson are with the Department of Preventive Medicine and Environmental Health, University of Iowa, Iowa City, IA, USA. Address correspondence to Dr Cantor, Environmental Epidemiology Branch, National Cancer Institute, Executive Plaza North, Suite 443, Bethesda, MD 20892, USA. Supported in part by United States National Cancer Institute research contracts (NCI-NO1-CP-51026 and NCI NO1-CP-85614) and by a Public Health Service Preventive Oncology Academic Award (5 KO7 CA01181-05). |
