[Mammary hamartoma with atypical stromal cells: a potential diagnostic dilemma].

Hamartoma of the breast is a pseudotumoural lesion that does not usually pose diagnostic problems for the pathologist. Although atypical stromal cell (ASCs) can be encountered in several benign and malignant breast lesions, their occurrence in hamartoma has not been reported to date. The authors report a case of breast hamartoma containing numerous atypical mono- or multinucleated stromal cells within the fibro-fatty component. This unusual feature raised differential diagnostic problems with pleomorphic lipoma, well-differentiated liposarcoma and malignant phylloid tumour with a lipomatous heterologous component. Immunohistochemistry, showing positivity to vimentin and CD34, revealed that ASCs are fibroblastic in nature, and thus are likely to represent a morphological variant of the fibroblasts of the native mammary stroma.