Myoepithelial carcinoma of the breast arising in adenomyoepithelioma. A case report.

Abstract

Introduction: Adenomyoepithelioma (AME), and especially myoepithelial carcinoma (MC), the malignant variant of this tumor, is a rare breast neoplasm. This report comprises the pathological features of a breast MC arising in AME with an aggressive clinical course. Case report: A 48-year old woman with a palpable mass in the right breast was admitted in November 1998. A month later following FNAB, surgical excision was performed. During the follow-up period of 17 months, until the patient's death, two local recurrences developed. Despite the aggressive chemotherapy, administrated after the first recurrence, subsequently bone, pulmonary and brain metastases appeared. Results: The primary tumor was an ovoid, white-grey, encapsulated mass measuring 4x3,5x1,5 cm. Microscopically, this biphasic tumor was composed of rare tubules surrounded by interlacing bundles of spindle cells exhibiting mild atypia. It was initially classified as a benign phyllodes tumor. The immunohistochemical analyses performed after the second recurrence proved the myoepithelial origin of the neoplasm (S-100, cytokeratin and alpha-SMA positive cells), with a high mitotic index (11 MF/10 HPF), and an immunophenotype indicating aggressive biological potential (steroid receptor negative, 50% Ki-67 and 30% p53 positive cells). Therefore, it was reclassified as MC arising in spindle cell type of AME. Conclusion: The histopathological diagnosis of AME could be very difficult, especially when a distinction from other spindle cell breast neoplasms must be done. Immunohistochemistry is essential to confirm the diagnosis, having in mind the reported pathological characteristics and the immunohistochemical profile of recurrent and malignant tumors of this type.