Histology of fibroadenomas include the following features:

• Two growth patterns are predominantly identified in classic fibroadenomas. These patterns do not carry much clinical significance.
  • Intracanalicular: glands are compressed into linear branching structures by proliferating stroma
  • Pericanalicular: glands retain open lumens but are separated by expanded stroma
• Glandular elements have intact myoepithelial cell layer

Complex fibroadenomas are a subtype of fibroadenomas with additional histologic features that can include:

1. Sclerosing Adenosis: Proliferation of acini with fibrosis.

2. Epithelial Calcifications: Calcium deposits within the epithelial cells.

3. Papillary Apocrine Changes: Papillary projections with apocrine metaplasia.

4. Cystic Changes: Formation of cysts within the fibroadenoma.

Usually has a peri-canalicular growth pattern.

Has increased relative risk of progression to breast carcinoma when compared to other variants of fibroadenoma.