Fibromatosis of the breast: a mimic of cancer

Clinical History

A 69-year-old female patient reported a painless lump in the right axillary tail of Spence found during self-examination approximately 1 year before. She had no relevant medical records.

Imaging Findings

On physical examination, a hard, mobile, non-tender mass was noted in the right axillary tail of Spence, with overlying skin retraction. There was no evidence of axillary or supraclavicular adenopathy.

Mammography revealed a focal density with spiculated margins in the right axillary tail of Spence, which was only partially depicted due to its location (Fig. 1).

Ultrasonography showed a circumscribed, hypoechoic mass with angular margins and slightly posterior acoustic shadowing (Fig. 2).

Contrast-enhanced MRI revealed a spiculated mass with rapid and avid contrast uptake, that was suspected to have accompanied involvement of the minor pectoralis muscle. It measured 46x28x23mm.

Due to it being highly suspicious for malignancy, ultrasound-guided core biopsy was performed, revealing intersecting fascicles of spindle cells with narrow, enlongated, slightly wavy nuclei, without atypia or mitosis compatible with fibromatosis of the breast.
The patient subsequently underwent wide local excision of the lesion and currently is waiting for her first follow-up examination.

Discussion

Fibromatosis of the breast, also called extra-abdominal desmoid, is a rare benign tumour, accounting for only 0.2% of all breast tumours [1]. They typically present as a diagnosis dilemma for clinicians, radiologists and surgeons as they are indistinguishable from malignancy not only on imaging and clinical findings but also on gross evaluation [2].

Its aetiology remains controversial: suggestions of its origin from within the breast parenchyma itself, from the aponeurosis overlying the pectoralis major muscle or even secondary to a previous history of breast surgery or trauma have been reported [3].

It is characterized by an infiltrative growth resulting in locally aggressive behaviour and frequent local recurrence, but no metastatic potential. It can affect a wide age range (13 to 83 years) [1]. Most commonly it occurs sporadically, but can also be associated with predisposing genetic syndromes (Gardner syndrome, familial multicentric fibromatosis and hereditary desmoid disease) [4].

Typically breast fibromatosis presents as a solitary, unilateral mass but multiple and bilateral lesions can be observed. The physical findings are a firm, palpable, well-defined mass that is frequently associated with skin retraction or dimpling [5].

Mammography often depicts an irregular-shaped, high-density non-calcified mass with spiculated margins, and no associated adenopathies [1-3].

Ultrasound usually reveals a solid, spiculated or microlobulated, irregular hypoechoic mass with a thick echogenic rim and posterior attenuation [6].

MRI is often useful to evaluate chest wall involvement and tumour extension. The appearance of fibromatosis is ill-defined, hypo to isointense on T1, heterogeneous with areas of high and low signal intensity on T2 with variable enhancement patterns [7].

As findings are non-specific and cannot exclude malignancy, biopsy (core needle or excisional) is required for a definitive diagnosis. Histologically, it consists of long fascicles of bland-looking spindle-shaped cells with variable amounts of intervening collagen [6, 8].

Breast fibromatosis is treated surgically, typically with wide local excision because of its locally invasive behaviour and recurrence potential, which is higher in those with positive margins. Other options might be radiation therapy or pharmacological treatment (e.g. antioestrogen therapy, NSAIDS, cytotoxic chemotherapy) [1-4].

Clinical and imaging follow-up is advised to monitor for recurrence [1].

Differential Diagnosis List

Final Diagnosis

Fibromatosis of the breast

URL:	https://eurorad.org/case/14638
DOI:	10.1594/EURORAD/CASE.14638
ISSN:	1563-4086