The boundaries of the benign spindle cell stromal tumors of the breast are still confusing. This is the reason why different names are interchangeably used for the same tumor and vice versa the same name for different tumors. Therefore we studied the immunoexpression of easily available markers, such as CD34, alpha-smooth muscle actin, desmin, with the addition of STAT6, as well as the chromosome 13q14 region by fluorescence in situ hybridization analysis in a series of 19 cases of benign spindle cell stromal tumors of the breast. Based on the morphological and immunohistochemical findings the following histotypes were identified: i) tumors (10 out of 19 cases) with the characteristic morphology of myofibroblastoma and stained with vimentin, CD34, desmin and α-smooth muscle actin; ii) fibroblastic benign spindle cell tumors (5 out of 19 cases) composed of fibroblast-like cells stained only with vimentin and CD34; iii) tumors (2 out of 19 cases) with the typical morphological features of solitary fibrous tumor and stained with vimentin, CD34 and STAT6; iv) one case of spindle cell lipoma stained with vimentin and CD34; v) one case of fibroma composed of a paucicellular, diffusely hyalinized stroma with expression of vimentin and CD34. Notably most of the tumors, with the exception of solitary fibrous tumor, showed monoallelic deletion of FOXO1. This finding supports that myofibroblastoma, fibroblastic benign spindle cell tumor, spindle cell lipoma and fibroma of the breast are histogenetically-related lesions which belong to the same tumor entity.
- 13q14 Deletion
- Benign Spindle Cell Tumors