Fibromatosis of the breast

Last revised by Henry Knipe on 10 Nov 2021

Fibromatosis of the breast, also known as an extra-abdominal desmoid tumor of the breast or mammary fibromatosis 4, is considered a rare breast tumor. It is a non-metastasizing benign but locally invasive stromal tumor 4. However, it can mimic more sinister types of breast cancer on both imaging and clinical findings 8.

They account for only 0.2% of all breast tumors 9.

A desmoid tumor appears as a solitary, hard and painless nodule, which sometimes can be attached to the skin or to the pectoral muscle fascia.

The entity is pathologically indistinguishable from fibromatosis occurring elsewhere in the body. The tumor has a fibroblastic and myofibroblastic origin.

Recognized associations include:

  • while it can occur anywhere in the breast, lesions may tend to occur in close proximity to pectoral muscles

A spiculated, irregular, non-calcified mass is considered the most common mammographic finding.

Fibromatosis typically appears as a solid, spiculated or microlobulated, irregular hypoechoic mass with straightening and tethering of Cooper ligaments, which is very difficult to differentiate from a malignant lesion.

Usually seen as an irregular breast mass.

  • T1: mammary fibromatosis may appear as ill-defined, hypo- to isointense masses
  • T2: usually heterogeneously hyperintense in signal
  • T1 C+ (Gd): often show suspicious, slow enhancement after contrast administration 

MRI is often useful to show chest wall involvement in selected cases prior to surgical planning.

Although it is a benign non-metastasizing tumor, it can be locally aggressive. Wide local excision with clear margins remains the treatment of choice 5. Recurrence rates can be high, especially in those with positive margins. Recurrence is less likely if a wide excision is performed and resection margins are made sure to be disease-free. Recurrences are also often treated with radical excision, like the primary tumor.

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Cases and figures

  • Case 1a: mammography
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  • Case 1b: PET CT
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  • Case 2
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