Fibroadenomas are benign breast tumours characterized by an admixture of stromal and epithelial tissue. Breasts are made of lobules (milk producing glands) and ducts (tubes that carry the milk to the nipple). These are surrounded by glandular, fibrous and fatty tissues. Fibroadenomas develop from the lobules. The glandular tissue and ducts grow over the lobule to form a solid lump. Since both fibroadenomas and breast lumps as a sign of breast cancer can appear similar, it is recommended to perform ultrasound analyses and possibly tissue sampling with subsequent histopathologic analysis in order to make a proper diagnosis. Unlike typical lumps from breast cancer, fibroadenomas are easy to move, with clearly defined edges. Fibroadenomas are sometimes called breast mice or a breast mouse owing to their high mobility in the breast. Signs and symptoms Fibroadenomas are benign tumours of the breast, most often present in women in their 20s and 30s. Clinically, fibroadenomas are usually solid breast lumps that are: • Painless • Firm or rubbery • Mobile • Solitary-round with distinct, smooth borders People who have a simple fibroadenoma have a slightly increased risk of developing malignant (harmful) breast cancer. Complex fibroadenomas may increase the risk of breast cancer. In the male breast, fibroepithelial tumors are very rare, and are mostly phyllodes tumors. Exceptionally rare case reports exist of fibroadenomas in the male breast, however these cases may be associated with antiandrogen treatment. Cause The cause of fibroadenoma is unknown (idiopathic). A connection between fibroadenomas and reproductive hormones has been suggested which may explain why they present themselves during reproductive years, increase in size during pregnancy, and regress post-menopause. Higher intake of fruits and vegetables, higher number of live births, lower use of oral contraceptives and moderate exercise are associated with lower frequency of fibroadenomas. Pathology Cytology The diagnostic findings on needle biopsy consist of abundant stromal cells, which appear as bare bipolar nuclei, throughout the aspirate; sheets of fairly uniform-size epithelial cells that are typically arranged in either an antler-like pattern or a honeycomb pattern. These epithelial sheets tend to show typical metachromatic blue on Diff-Quik staining. Foam cells and apocrine cells may also be seen, although these are less diagnostic features. The gallery images below demonstrate these features. Cellular fibroadenoma, also known as juvenile fibroadenoma, is a variant type of fibroadenoma with increased stromal cellularity. Macroscopic Approximately 90% of fibroadenomas are less than 3 cm in diameter. However,