Fascicular spindle cell growth irregularly infiltrating surrounding fatty breast tissue. Mild to moderate cellularity is seen.

An entrapped small ductal structure remains here surrounded by fibromatosis.

Similar to abdominal desmoid, fibromatoses of the breast is composed of fibroblasts forming fascicles that infiltrate the breast parenchyma. There is little or no mitotic activity. Lymphoid follicles may be seen at the periphery of the lesion.

Typically occur in premenopausal women (2nd through 4th decade), but can be seen in a wide age range.

Although this is a benign process that cannot metastasize, recurrence rate is high, especially if a wide excision with a 1 cm margin was not performed.