Male breast cellular myofibroblastoma with a rich reticulinic network: case report.

Myofibroblastoma is a rare mesenchymal tumor located not only in breast but also in extramammary sites. This is the 79th case of breast myofibroblastoma reported in the literature. This tumor presents a great variety of morphological features, which increase the difficulty of differential diagnosis. The authors report a breast myofibroblastoma diagnosed in a 73-year-old male. The article discusses a bilateral gynecomastia and a palpable right breast well-defined tumor, without calcifications on mammography, which was surgically removed. Macroscopically, a well-circumscribed uncapsulated nodule was seen with lobular arrangement on cut section, and microscopically, a nodule with pushing borders and a connective pseudocapsule was seen. The spindle cells were arranged in fascicular clusters, with focally collagen bundles and a rich reticulinic network stained black with Gömöri impregnation. Immunohistochemically, the tumor cells were marked by vimentin, CD34, desmin, and smooth muscle antigen and did not express cytokeratin, S-100 protein, CD99, CD10, and factor VIII-related antigen. More than 90% of the cells expressed estrogen receptor. No recurrences were reported 2 years after surgical excision. This case is a variant of cellular myofibroblastoma, with a rich reticulinic network and scanty collagen bands.