The tumor cells of the mural nodule were strongly positive for cluster of differentiation 10 (CD10) and progesterone receptor (PR) and was negative for cytokeratin 7 (CK7), CK20, estrogen receptor (ER), a-inhibin, calretinin, caldesmon, and smooth muscle actin (SMA), which is a typical feature of endometrial stromal sarcoma. The gene discussed is PGR; the disease is neoplasm.