Histopathology of Fibroadenoma of the Breast

The aim of this study was to make a thorough inventory of the histologic features of epithelium and stroma within and adjacent to breast fibroadenomas in 396 cases. Breast fibroadenomas seemed to display a wide spectrum of proliferative and nonproliferative histologic changes. Hyperplasia (excluding mild hyperplasia) within the fibroadenoma was found in 32.3% of cases. Carcinoma in situ (CIS; 5 ductal, 3 lobular) was found in 8 fibroadenomas (2.0%) removed from 6 patients, the youngest of whom was 40 years of age. In 3 cases CIS was not confined to the fibroadenoma, but also involved the adjacent parenchyma. No invasive carcinoma was present within this series. Complex histologic features were seen in 40.4% of cases, mostly in relatively older patients (mean age, 35.4 years). Hyperplasia in adjacent tissue was found in 8.8% of cases, usually in older patients (mean age, 45.5 years). Known risk-elevating lesions in and around breast fibroadenomas occur frequently and mostly in patients older than 35 years. These findings may have consequences for the clinical management of a subgroup of patients with fibroadenoma. Fibroadenoma of the breast is a relatively frequently occurring tumor. It can occur in women of any age, but the peak incidence is during the second and third decades of life. 1 Although often considered a benign tumor, several reports describe a higher risk of subsequent breast carcinoma in patients diagnosed with fibroadenoma. 2-5 Dupont et al 2 found relative risks (RRs) ranging from 2 to 4, depending on the presence of complex changes within the fibroadenoma, benign proliferative disease in the surrounding parenchyma, and a positive family history of breast cancer. For hyperplasia in the surrounding tissue, this was demonstrated previously by McDivitt and coworkers. 4 In addition, the development of invasive carcinoma within fibroadenoma has been well docu