Background: Fibroadenomas are benign breast tumors that are commonly diagnosed in young women and are associated with a slight increase in the risk of breast cancer. These lesions vary considerably in their histologic characteristics. We assessed the correlation between the histologic features of fibroadenomas and the risk of subsequent breast cancer.
Methods: We conducted a retrospective cohort study of a consecutive series of patients with fibroadenoma diagnosed between 1950 and 1968. Follow-up data were obtained for 1835 patients (90 percent of those eligible). Fibroadenomas with cysts, sclerosing adenosis, epithelial calcifications, or papillary apocrine changes were classified as complex. The rate of subsequent breast cancer among the patients was compared with the rates in two control groups, women listed in the Connecticut Tumor Registry and women chosen from among the patients' sisters-in-law.
Results: The risk of invasive breast cancer was 2.17 times higher among the patients with fibroadenoma than among the controls (95 percent confidence interval, 1.5 to 3.2). The relative risk increased to 3.10 among patients with complex fibroadenomas (95 percent confidence interval, 1.9 to 5.1) and remained elevated for decades after diagnosis. Patients with benign proliferative disease in the parenchyma adjacent to the fibroadenoma had a relative risk of 3.88 (95 percent confidence interval, 2.1 to 7.3). Patients with a family history of breast cancer in whom complex fibroadenoma was diagnosed had a relative risk of 3.72, as compared with controls with a family history (95 percent confidence interval, 1.4 to 10). Two thirds of the patients had noncomplex fibroadenomas and no family history of breast cancer and did not have an increased risk.
Conclusions: Fibroadenoma is a long-term risk factor for breast cancer. The risk is increased in women with complex fibroadenomas, proliferative disease, or a family history of breast cancer.