Since we presented an inguinal subcutaneous tumor mass with a postoperative pathological diagnosis of ectopic endometriosis occurring in the uterine round ligament, the purpose of the immunohistochemical analysis in this case report is to compare the stainability of newly applied antibodies to conventional antibodies against CA125, estrogen, and progesterone receptors, to reveal the mechanism of the disease, and to determine the most sensitive procedure for detecting an ectopic endometrial tissue. The gene discussed is PGR; the disease is neoplasm.