Aggressive Angiomyxoma of the Pelvis with a Cellular Nodule Composed of Tumor Cells showing Epithelioid Features.

A 49-year-old female presented with an aggressive pelvic angiomyxoma (AAM). The completely resected specimen revealed the usual myxedematous tumor with a nodule inside it. Histopathologically, the myxedematous area consisted of bland spindle-shaped cells in the background of blood vessels of varying calibers, and the nodule was composed of tumor cells with epithelioid features. In the nodule, cellularity was increased and nuclear enlargement was observed, but nuclear atypia was not significant and mitotic figures were scarce. Immunohistochemically, both components were positive for desim, αSMA, estrogen receptors, and progesterone receptors. However, they were negative for AE1/3, EMA, S100, CD34, HMB45, and Melan A. The MIB-1 labeling index was 5.8% in the nodule and 1ess than 1% outside it. The nodule was therefore considered a benign component of AAM. To the best of our knowledge, the presence of such a nodule in AAM has not been reported previously.