Fibromatosis (also called desmoid tumor) is a rare benign growth of the breast’s stroma (or connective tissue) made up of spindle-shaped cells that closely resemble normal breast cells. It is locally invasive, meaning that it grows into nearby healthy tissue, but it doesn’t spread to other parts of the body. Fibromatosis often surrounds the ducts and lobules of the breast, forming a lump that can be felt through the skin. You also may notice an indent or dimpling of the breast skin or the area may appear to be stuck to the underlying muscle.
On a mammogram, fibromatosis looks just like breast cancer. Biopsy is needed to make the correct diagnosis. The treatment for fibromatosis is wide local excision — surgery to remove the growth itself along with a margin of normal tissue. There is a risk of the tumor recurring if any cells are left behind.