Breast Fibromatosis, A Rare Benign Tumor Mimicking Breast Carcinoma: A Case Report

Objectives: Fibromatosis is a rare breast lesion that is considered locally aggressive tumor without metastasis. It doesn't need more than surgical excision with clean margins as a treatment but the recurrence is very common. Breast fibromatosis clinically mimics other lesions as fibromatosis like metaplastic tumor of breast. Therefore, recognition of breast fibromatosis is important for surgeons and histopathologists, in order to set a proper plan for management and avoid unnecessary extensive surgery. Comprehensive search revealed only 33 case reports as it's compromising less than 0.2% of all primary breast tumor. Case summary Methods and Materials: A 35 years old female patient complained of palpable left breast mass for four months. Her imaging belonged to BI-RAD (4) assessment category. The pathological examination of the core biopsy showed B3; spindle cell lesion. The patient underwent surgical excision of the mass and the histopathologic assessment revealed an infiltrative uncapsulated lesion composed of proliferated spindle shaped cells (mixed fibroblasts and myofibroblast like cells) arranged in sweeping fascicles with occasional extravasated RBCs. There was no mitosis, necrosis or atypia. There was no associated hyperplasia, atypical hyperplasia, insitu or invasive components. Results: Immunohistochemical studies showed positivity for SMA and B- Catenine and negativity for Pan CK and P63 that confirm our diagnosis. Conclusion: The conclusion of this case report is to stress upon keeping breast fibromatosis in mind as a potential differential diagnosis for fibromatosis like metaplastic carcinoma and other mimics of spindle cell lesions in breast.