Breast Fibromatosis

Breast fibromatosis, also called desmoid fibromatosis of the breast or a desmoid tumor of the breast, is a tumor that forms in the breast’s connective tissue, called the stroma. Breast fibromatosis is rare: about 0.2% of breast tumors are desmoid tumors of the breast. While anyone can be diagnosed with them, these tumors are two to three times more common in people assigned female at birth.

Desmoid tumors can form anywhere in the body. Besides the breast, common sites include the abdomen, the head and neck area, trunk, and the hands and feet.

Breast fibromatosis isn’t considered malignant because these tumors don’t spread to other parts of the body (metastasize). But breast fibromatosis also isn’t truly benign because it can be locally aggressive and often regrows in the breast area after surgery to remove it (local recurrence).

The causes of breast fibromatosis aren’t clear. Some studies have found a link between breast fibromatosis and a history of breast trauma, breast surgery, or pregnancy. Research suggests many desmoid tumors occur randomly and may happen when stroma cells develop a mutation in the CTNNB1 gene.

Many, but not all, breast fibromatosis tumors form a lump you can feel through your skin. The lump may or may not be painful. The breast skin also may develop an indent or dimpling. 

If you or your doctor feel a lump, your doctor does a physical exam and asks about your medical history.

On a mammogram, a breast fibromatosis tumor looks like breast cancer. Studies suggest that ultrasound may be better than a mammogram for diagnosing breast fibromatosis, but a biopsy is needed to make the final diagnosis. Most researchers recommend a core needle biopsy rather than a fine needle aspiration biopsy.

In the past, surgery was considered the main treatment for breast fibromatosis. But because breast fibromatosis has a high risk of coming back in the breast area, surgery to remove the tumor is now somewhat controversial. Each local recurrence may mean another surgery, and each additional surgery ups the risk of complications and may make breast reconstruction, if someone wants that option, difficult.

The National Comprehensive Cancer Network (NCCN) doesn’t have treatment recommendations specifically for desmoid tumors of the breast. For desmoid tumors in areas where their growth wouldn’t cause death, which includes the breast area, the NCCN recommends careful observation until tumor growth causes problematic symptoms, like pain, or limits function. Observation means imaging with ultrasound or MRI every three months. If the tumor grows, surgery alone, surgery followed by radiation, radiation alone, medicine, or ablation (using heat or cold to kill the tumor cells) may be treatment options.

Chemotherapy isn’t regularly used to treat breast fibromatosis, but may be recommended if the tumor is growing rapidly and causing symptoms. Targeted therapy also isn’t currently used to treat breast fibromatosis, but clinical trials are studying new medicines that may be beneficial.

Because a breast fibromatosis tumor has a high risk of recurrence, follow-up care is important. Experts recommend MRI or ultrasound scans every three to six months for the first two years after diagnosis and then yearly MRI scans after that.