A panel of immunohistochemical markers were utilized to exclude the differentials, which included biphasic mesothelioma (calretinin), germ cell tumor (SALL4), biphasic synovial carcinoma (CD99, bcl - 2, TLE1), and a metastatic deposit of a carcinosarcoma/metaplastic carcinoma from the female genital tract (PAX8) and breast (GATA 3). The gene discussed is CD99; the disease is carcinosarcoma.