Fibroadenoma masquerading carcinoma on fine-needle aspiration of the breast

Objective: Benign and malignant lesions of the breast may have similar appearances on fine-needle aspiration cytology We report a case of fibroadenoma that was diagnosed as carcinoma by cytology. Case study: Breast fine-needle aspiration biopsy was highly cellular and composed of bland-appearing spindle/columnar cells that could represent either epithelial or stromal cells; the case was reported as positive and the patient had subsequent excisional biopsy taken. Results: On microscopic examination, smears were hypercellular and had many single cells and clusters of columnar/elongate cells No obvious bipolar cells of myoepithelial origin were seen. Significant atypia was noted. Immunocytochemistry for smooth muscle actin was not performed due to insufficient material. Conclusions: Some cases of fibroadenoma and carcinoma can be very difficult to distinguish on fine needle aspiration cytology smears. Immunocytochemistry may be of help if sufficient material is provided. To avoid false positive diagnosis on cytology, it is best to report such a case as intermediate (atypical/suspicious) with final interpratation pending excisional biopsy.