Desmoid-type Fibromatosis of the Breast Mimicking Carcinoma

Summary

A 43-year-old female with left-sided mastodynia was referred to our department for magnetic resonance imaging (MRI). Her surgical history included an excisional biopsy of a fibroadenoma in the left breast. On MRI, no explanation for the clinical complaints could be found. However, an enhancing stellate lesion (7 mm) at 9 oÂ’clock in the contralateral right breast was noted. On mammography of the right breast, a focal asymmetric density with spiculated margins was seen in the superolateral quadrant. There were no associated microcalcifications or suspicious lesions elsewhere. A second-look ultrasound in this region demonstrated a small oval hypoechoic mass (4 mm) with partially obscured borders. This lesion was categorized as a BI-RADS 4b lesion, and core needle biopsy was advised. Histological analysis revealed an infiltrative stromal process with interlacing bundles of fibroblast and myofibroblast, suggestive for a desmoid tumor. Wide excision was recommended and confirmed fibromatosis. A desmoid tumor can occur anywhere in the breast, but tends to be in close proximity to the pectoralis major muscle, arising from the pectoral fascia. Patients can be asymptomatic or present with a painless and firm mass. The lump may be fixed to the chest wall if originating from the pectoral fascia. Occasionally, associated skin thickening and retraction is noted. Imaging characteristics are non-specific. On ultrasound, mammography and MRI, fibromatosis manifests as a suspicious solid mass with irregular and spiculated borders, making it difficult to differentiate from primary breast malignancy. Treatment consists of wide local excision, considering the high local recurrence rate after incomplete surgical resection. Desmoid-type fibromatosis is a mimicker of malignancy, with suspicious morphological findings on all imaging modalities due to the local infiltrative characteristics. Dynamic features on MR imaging may suggest a benign entity, but nonetheless, a biopsy remains the appropriate approach to rule out a primary breast tumor.