A 35-yrs-old woman presents with a 2.2 -cm mass in her left breast. The mass is excised, and histologic sections reveal a tumor composed of a mixture of ducts and cells. The epithelial cells within the ducts are not atypical in appearance. There is a marked increase in the stromal cellularity, but the stromal cells are not atypical in appearance and mitoses are not found. Which of the following is the most likely diagnosis?: (A) Atypical epithelial hyperplasia, (B) Benign phyllodes tumor, (C) Fibroadenoma, (D) Malignant phyllodes tumor
Answer is B. Benign phyllodes tumor * Neoplastic proliferations of the stroma of the breast may lead to the formation of either fibroadenomas or phyllodes tumors. * Fibroadenomas are characterized histologically by a mixture of fibrous tissue and ducts, with no increase in cellularity or mitoses. * Only the stromal cells, not the glandular cells, are clonal proliferations. Another neoplastic tumor that arises from the stromal cells is the phyllodes tumor. * It is distinguished from fibroadenomas by a more cellular stroma and the presence of stromal mitoses. The phyllodes tumor, which has been called a cystosarcoma phyllodes, may either be benign or malignant. * A benign phyllodes tumor is characterized by increased stromal cells with few mitoses, while a malignant phyllodes tumor has increased numbers of stromal cells that are atypical along with numerous mitoses.