Malignant Phyllodes Tumor of the Breast With Multiple Cutaneous Metastasis Resembling Pleomorphic Rhabdomyosarcoma.

Abstract: Malignant phyllodes tumor (PT) of the breast is a rare fibroepithelial neoplasm that shows variegated histomorphology and an aggressive clinical course. Cutaneous metastases are rare. A 68 year old woman presented with a palpable left breast mass identified on a routine breast exam. Mammogram showed an oval circumscribed heterogeneous mass measuring 3.7 × 3.7 × 2.7 cm. Patient underwent core needle biopsy with subsequent excision and received a diagnosis of malignant phyllodes tumor with rhabdomyosarcomatous elements with negative margins. The patient suffered a local recurrence 5 months later and was scheduled for re- excision; however prior to that procedure the patient represented to clinic with several cutaneous and subcutaneous nodules located on the left flank, left arm, and bilateral buttocks; described as itchy but not painful. Biopsies of the left flank and the left arm were performed and pathologic examination of both biopsies demonstrated a high- grade rhabdomyoblastic neoplasm that closely resembled so-called pleomorphic rhabdomyosarcoma. The tumor cells in both biopsies marked for immunohistochemical markers of rhabdomyoblastic differentiation and re-review of the original resection specimen showed identical areas confirming the skin and subcutaneous nodules as metastatic malignant phyllodes tumor. We report an unusual case of malignant PT with cutaneous metastases that demonstrated a pure rhabdomyosarcoma phenotype with pleomorphic morphology. Awareness that malignant PT may rarely involve cutaneous sites and present with a pure rhabdomyosarcomatous morphology is important for proper recognition and diagnosis of these tumors, as out of context they may be confused with sarcomas.