Primary rhabdomyosarcoma of the breast in a teenager: a case report

Although rhabdomyosarcoma (RMS) is the most common soft-tissue neoplasm in children, primary breast rhabdomyosarcoma is rare, as breast involvement typically occurs through secondary metastasis rather than as a primary tumor. A 14-year-old girl presented with a progressively enlarging swelling in her left breast over eight weeks. It began as a small, peanut-sized lump that gradually increased in size, followed six weeks later by a left axillary swelling. She sought medical care eight weeks after the breast swelling began. At presentation, she reported fatigue, weight loss, loss of appetite, and night sweats. On examination, she was malnourished (BMI 18.1 kg/m 2 ). A firm, non-tender left breast mass measuring 5 × 4 cm was palpated, fixed to underlying tissue but not adherent to the skin. A hard, non-tender left axillary lymph node measuring 2 × 1.5 cm was also noted, while the right breast and axilla were normal. Ultrasound and fine-needle aspiration cytology (FNAC) revealed an undifferentiated high-grade malignant tumor with axillary metastasis. Given lymphatic spread, the disease was considered advanced, and chemotherapy with Adriamycin and cyclophosphamide was initiated. Because other malignancies such as high-grade non-Hodgkin lymphoma and dysgerminoma were possible, an incisional biopsy was performed before mastectomy. Histopathology showed small round blue cells, and immunohistochemistry confirmed rhabdomyosarcoma. After diagnosis, the prognosis and treatment options, including radical mastectomy with lymph node dissection, were discussed with the patient and her family. However, they declined surgery and continued chemotherapy alone. One month later, she returned for her second chemotherapy cycle but had developed back pain and severe debilitation. She did not return afterward and passed away two months later. Breast rhabdomyosarcoma should be considered in the differential diagnosis of unexplained or rapidly enlarging breast swelling, particularly in young patients. • Less than 1% of primary breast cancers are sarcomas, and breast involvement—primary or metastatic is very rare. • Primary breast sarcomas, including rhabdomyosarcoma, often appear as large, painless masses that grow rapidly. • Diagnosis requires history, exam, imaging, FNAC, biopsy, and immunohistochemistry. • RMS shows small round blue cells with distinct patterns; desmin, myogenin, MyoD1, and PAX3-FKHR confirm diagnosis. • Surgery is the main treatment; radiotherapy and chemotherapy have limited roles, and delayed diagnosis worsens prognosis.