A 23-years-old female patient, with a previous surgical reconstruction with right implanted breast prosthesis for a congenital malformation of the chest wall, presented for palpable mass in the upper-external quadrant near the right breast prosthesis. She had mastalgia without thelorrhagia. No suspicious axillary lymph nodes were detected at clinical examination.
Ultrasound revealed a solid mass with irregular margins and posterior acoustic shadowing near the prosthesis. No suspicious axillary lymph nodes were detected. Silicotic granuloma and breast cancer were proposed as differential diagnosis, and further examination with magnetic resonance imaging (MRI) was proposed. MRI revealed strong and irregular non-mass enhancement after administration of gadolinium-based contrast agent, in contact with the capsule of the prosthesis. The dynamic contrast curve was type three. The suspicious characteristics suggested further examination, with core needle biopsy, that was inconclusive. Surgical excision was proposed to the patient and pathologic-anatomy histology revealed a focal desmoid-type fibromatosis.
Desmoid-type fibromatosis (DTF) is a rare benign lesion, with local aggressiveness, that can arise anywhere in the body. In the breast [1, 2] the differential diagnosis from primary breast cancer is challenging. The mammographic, ultrasound and magnetic resonance imaging (MRI) findings  can mimic breast malignancy, suggesting that an accurate diagnosis of DTF must be made with histology. 
It is mainly sporadic but can be associated with familial adenomatous polyposis (FAP), and the association of desmoid tumors and FAP is known as Gardner syndrome. 
Surgical scars and hormonal factors (pregnancy) are risk factors for the development of such lesions.  Cases of mammary DTF described in literature are typically around silicone breast implants. 
The most frequent clinical presentation of DTF is a slow-growing painless soft-tissue mass, but it depends on the anatomical location and can lead to fatal cases of mesenteric desmoid tumours.
The absence of typical imaging characteristics imposes histological evaluation for the final diagnosis, better if confirmed by an expert soft tissue pathologist. 
As described by other authors, our case was interpreted as a primitive malignant lesion. The presence of DTF could have been suspected in the presence of breast implants and prior surgery, which are risk factors for the development of this type of lesion, associated with absence of personal history of primary malignant breast lesions and the young age of our patient.
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