Fibromatosis of the breast is an uncommon, poorly demarcated, locally aggressive neoplasm originating from fibroblasts and myofibroblasts within the breast parenchyma. The neoplastic cells are spindle-shaped and arranged in interlacing fascicles. A characteristic feature are infiltrating finger-like projections at the periphery of the lesion which entrap mammary ducts and lobules. The tumour presents as a solitary, painless, firm, palpable mass measuring 0.5 to 10 cm (average 2.5 cm). It may be associated with skin or nipple retraction and rarely with nipple discharge. The mammographic appearance is that of a carcinoma.
Mammary fibromatosis is very rare (<0.2% of all breast lesions). It affects most commonly women in the childbearing age, but has been reported in patients from 13 to 80 years of age. A few cases have been found in men. The tumour has no metastatic potential. The tendency for local recurrence is around 25% and thus significantly lower than for extramammary fibromatoses (around 57%)
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