Objective  To investigate the clinicopathological features and differential diagnosis of fibromatosis of the breast.

  Methods  Five cases of breast fibromatosis were reviewed based on clinical, histomorphological, and immunohistochemical studies. Their clinical manifestations, pathologic features and main points of differential diagnosis were discussed.

  Results  The 5 cases were all females, with age of onset ranging from 24 to 75 years and an average age of 53 years. Three cases underwent breast focal biopsy, and 2 cases underwent simple mastectomy. Breast fibromatosis was composed of spindle cells (fibroblasts/myofibroblasts) in a background of numerous thick and wavy collagen fibers, showing various degrees of hyaline degeneration. The cells varied in number, but all with absence or low degree of pleomorphism and hypercellularity, and scarcity of mitotic figures. According to immunohistochemical study, the 5 cases were all vimentin positive and SMA partly positive, 3 cases were β-catenin positive, while cytokeratin, desmin, EMA, S-100 and CD68 were negative.

  Conclusion  Fibromatosis of the breast is a rare breast tumor, developing in a progressive and invasive pattern.