Incidental Detection of Carcinoma In-situ in Fibroadenoma of the Breast in a Young Woman: A Rare Finding

Fibroadenoma, being a very common benign tumor of the breast in young females, does not pose any threat and, thus, can be treated with lumpectomy. Breast cancer arising within a fibroadenoma is a rare phenomenon, but detecting these neoplasms is of utmost importance for complete treatment and follow-up. These lesions are an incidental finding in a lumpectomy specimen done for fibroadenoma breast. A 28-year-old female presented with multiple bilateral lumps for eight years. The lumps were mobile, non-tender, and slowly growing, with no nipple discharge, no axillary lymphadenopathy, and no family history. The diagnosis of a benign lesion suggestive of fibroadenoma was given on ultrasonography (USG) and fine-needle aspiration cytology (FNAC). The patient underwent lumpectomy and the excised tissues were subjected to histopathological examination. Grossly, multiple, well-circumscribed, encapsulated masses, with the largest measuring 4x2.5x2 cm were noted. All masses showed homogenous grey-white areas with slit-like spaces. On microscopy, predominant areas were consistent with fibroadenoma, with few foci showing the features of ductal carcinoma in situ (DCIS) with nests of cells having pleomorphic nuclei, prominent nucleoli with atypical mitosis, a cribriform pattern, and comedo necrosis. This highlights the rare association of fibroadenoma and carcinoma in situ, thus, a careful and extensive sampling of the tissue is required to prevent the false negative diagnosis by pathologists.