Recurrent Myopericytoma of the Breast Mimicking Phyllodes Tumour: A Diagnostic and Management Challenge.

BackgroundMyopericytoma is a rare perivascular neoplasm typically found in the extremities, with only a single previous case report in breast.Case PresentationWe describe a 37-year-old woman presenting with a recurrent left breast mass, initially suspected to be a phyllodes tumour based on clinical and radiological features. Histologic examination revealed a spindle cell neoplasm with concentric perivascular growth, focal necrosis, brisk mitotic activity, and tumour infiltration into the adjacent breast. Immunohistochemistry confirmed positivity for smooth muscle actin and vimentin with a Ki-67 index of 15%-20%, consistent with myopericytoma. The short-interval recurrence, invasive features, and high mitotic activity raised concern for malignant myopericytoma.ConclusionThis being only the second reported breast myopericytoma case report, highlights the diagnostic difficulty and emphasizes the importance of thorough pathologic and immunophenotypic assessment to distinguish it from more common spindle cell tumours of the breast and to guide appropriate surgical management.