Myofibroblastoma of the breast in a 5-year-old girl: A case report.

Myofibroblastoma is a rare, benign spindle cell tumor originating from the breast stroma. Although it predominantly affects older men and occasionally postmenopausal women, its occurrence in children is exceedingly rare. A 5-year-old girl presented with a palpable mass on the lateral aspect of her left breast. Serial ultrasound examinations were conducted every 6 months for 1 year because the lesion was initially suspected to be a lipoma or an enlarged lymph node. Owing to progressive enlargement of the mass to 3 cm, surgical excision was performed. A well-defined yellow-white solid mass located in the subcutaneous layer was completely removed. The histopathological and immunohistochemical findings confirmed the diagnosis of a myofibroblastoma. The postoperative course was uneventful, and no recurrence has been reported to date. Although extremely rare, myofibroblastoma should be considered in the differential diagnosis of enlarged breast masses in children. Complete surgical excision is the treatment of choice, and regular follow-up is recommended.