Clinico-pathological features of breast myxoma: report of a case with histogenetic considerations

We herein report the clinical, radiological, and pathological findings of a rare case of myxoma occurring in the breast parenchyma of a 75-year-old female. The tumor was incidentally detected at a mammographic screening and, ultrasonographically, presented as an ovoid mass. Histologically, an encapsulated hypocellular, myxoid tumor with low vascularization was evident. Neoplastic cells were round- to spindle/stellate-shaped and stained with vimentin and focally with calponin. We emphasize that morphology remains preeminent in the diagnosis of a breast myxoma, while immunohistochemistry may assist in ruling out other tumor entities. Differential diagnosis with all benign and malignant myxoid lesions, primarily occurring in the breast, is provided. The histogenesis of breast myxoma is unknown. The lack of expression of desmin, α-smooth muscle actin, CD34, CD99, CD10, bcl-2 protein, and estrogen/progesterone/ androgen receptors, all markers characteristically expressed by “the benign spindle cell tumors of the mammary stroma,” would suggest that breast myxoma does not fall into this tumor category and that its putative precursor mesenchymal cell resides in the interlobular stroma.