Risk Factors for Breast Cancer and its Prognosis

Abstract : This project investigated the influence of reproductive history on risk of breast cancer and its prognosis by taking advantage of very large linkages between population-based health and demographic registries in Denmark. Many of these registries have existed for several decades and contain mandatorily reported information, making very complete and long-term follow-up studies possible. A total of 18 studies were conducted during the study period. In 13 studies, the influence on breast cancer risk of induced abortion, age at birth, number of births, gender of child, multiple births, weight of child, alpha-fetoprotein level during pregnancy and family history was investigated in great detail. Breast cancer was not only investigated as a single outcome but also according to type, size of tumor at time of diagnosis, nodal spread, etc. Five studies dealt with factors that might influence the prognosis of breast cancer. Low age at first birth but not parity was associated with poor survival. A diagnosis of breast cancer less than 2 years after a child birth gave particularly poor survival. Young women had particularly poor survival but only those diagnosed with low-risk disease not receiving adjuvant cytotoxic therapy,-indicating that they would benefit from being given cytotoxic therapy in the future. A pregnancy subsequent to breast cancer did not aggravate the prognosis. Finally, we found a 20-30% difference in chance of survival depending on what quadrant in the breast the tumor was first diagnosed. Survival was most poor for tumors in the lower two quadrants, indicating that a more aggressive treatment approach might increase survival of those tumors.