Myofibroblastoma of the breast with hemangiopericytoma-like pattern and pleomorphic lipoma-like areas. Report of a case with diagnostic and histogenetic considerations.

Myofibroblastoma (MFB) of the breast is an uncommon benign spindle cell tumor which may exhibit a wide spectrum of histological features. We report an unusual case of MFB of the male breast, showing cellular areas with a hemangiopericytoma-like pattern similar to that observed in solitary fibrous tumor (SFT) and extensive fibromyxoid areas containing numerous atypical stromal cells. The association of these atypical cells with mature adipocytes and microcystic and/or myxoid degenerative changes resembled pleomorphic lipoma-like and myxoid liposarcoma-like features, respectively. To our knowledge, these peculiar morphological findings have not been previously reported in MFB of the breast. They should be recognized to avoid confusion with other mesenchymal tumors, especially with hemangiopericytoma, pleomorphic lipoma (PL), spindle-cell lipoma (SCL) and myxoid liposarcoma. A case of MFB of the breast showing morphological features also commonly seen in SFT and PL/SCL is further morphological evidence in support of the speculation that the mesenchymal tumors of the breast, also known under the terms benign spindle cell tumors, fibromas, SFTs, SCLs and MFBs, are histogenetically related lesions.