Recurrent Fibromatosis of the Breast

A 32-year-old female presented to our breast imaging center with a palpable abnormality in her right superior-lateral breast. Mammography and ultrasound demonstrated a spiculated mass. Subsequent biopsy demonstrated nodular fasciitis. The patient had an excisional biopsy in another country. Follow-up imaging demonstrated a recurrent enlarging mass invading the skin and pectoralis muscle.

Initial CC and MLO view of the right breast demonstrating a superior lateral focal asymmetry.

Ultrasound in the region of the palpable abnormality demonstrated well circumscribed anechoic structure with mildly irregular borders.

One year follow-up after excisional biopsy in another country, CC and MLO views of the right breast demonstrate an enlarging focal asymmetry in the same region of the previous biopsy, now involving the skin and pectoralis muscle.

Targeted ultrasound of the focal asymmetry demonstrates an enlarging mass with mixed echogenicity.

Axial pre and post contrast fat saturation, axial TRIM, and sagittal post contrast MRI images demonstrate an enhancing lesion invading the pectoralis muscle and dermis in the superior lateral right breast

One year post final resection CC and MLO views demonstrate post surgical changes without evidence of recurrence.

Discussion: Fibromatosis is extremely rare, with an incidence of less than 5 per million, comprising 3% of soft tissue tumors. These tumors usually affect the abdominal wall of parous women within 25 and 35 years of age. The mammary gland is one of the rarest sites in which fibromatosis has been described, representing a 4% of extra-abdominal lesions and only 0.2% of primary breast lesions. The mean age for diagnosis of breast fibromatosis is 42 years.

Clinically, breast fibromatosis presents as a firm palpable mass suspicious of malignancy that may adhere to the chest wall, sometimes with dimpling or retraction of the skin. It originates from the myofibroblasts and fibroblasts of the mammary gland parenchyma or from the musculo-aponeurotic layer of the chest wall extending into the breast. Fibromatosis developing in mammary gland parenchyma are less prone to recur (about 25%) than those that develop from the chest wall (about 57%). Most lesions arise in one of the mammary quadrants. Family history does not play an important role. Endocrine etiology is unlikely, as it has been reported that estrogen and progesterone receptors are not expressed in these cases, furthermore, breast fibromatosis is less commonly observed during or immediately after pregnancy.

A risk factor for these patients is trauma after surgical procedures, such as breast reduction or breast augmentation with silicone or saline implants, which have been associated in cases of breast fibromatosis. It is thought that breast fibromatosis can develop from the fibrous capsule surrounding breast implants, but the detailed etiology of breast fibromatosis remains unclear, as patients without prior surgery or known trauma have also developed these lesions.

These lesions are characterized as bland-appearing, non-encapsulated soft tissue tumor comprised of a fibroblastic and myofibroblastic spindle cell proliferation and collagen. These lesions do not metastasize but are characterized by local aggressiveness with infiltrative growth pattern and a high recurrence rate.

One of every three cases of breast fibromatosis demonstrates mammographic abnormalities. Demonstrated features include that of a carcinoma- irregular shape with high-density, spiculated margins and an absence of calcifications. Ultrasound often demonstrates a solid, microlobulated or spiculated mass, hypoechoic, with an echogenic rim. Margins are often irregular with no posterior acoustic shadowing. On computed tomography, an enhancing soft tissue mass demonstrating an isodensity or hypodensity in relation to surrounding skeletal muscle is seen. MRI is the best choice of imaging to determine with the boundaries of the tumor as well as a chest wall involvement. T1 weighted imaging will display a lesion isointense to skeletal muscle. T2 weighted imaging demonstrates heterogeneous lesions with varied intensity, including areas with similar intensity to skeletal muscle.

Macroscopically, the tumor is a gray-white colored lesion, irregular, firm, and poorly circumscribed. The histologic features are characterized by abundant collagen with surrounding bundles of spindle cells in an irregular fashion with regular nuclei. There is not a high mitotic activity rate, and cellularity varies from significant amounts of collagen to low cellular content peripherally. These lesions are commonly actin positive, vimentin positive, rarely positive for desmin, and negative for S100 and CD34. A positive reaction for ER and PR in a breast tumor would exclude breast fibromatosis as the diagnosis.

The differential diagnosis includes breast cancer, which can be mimicked clinically and on imaging, phylloides tumor, and high-grade fibrosarcoma. On cytology, phylloides tumor demonstrates hypocellularity, an epithelial component, and abundant collagen in the radial scar. High-grade fibrosarcoma displays a higher mitotic activity, cellularity, and pleomorphism.

There are significant clinical, radiologic, and histologic overlap among reactive and neoplastic lesions. Because no unique radiologic appearance of nodular fasciitis or fibromatosis has been reported, the exact diagnosis can be made only by histopathologic findings.

The most effective treatment for fibromatosis is primary surgical excision with negative margins, which significantly decreases the likelihood of recurrence.

Alan Alexander, MD, and Erini Makariou, MD, Georgetown University Hospital
Department of Radiology