CA 125 production in desmoplastic small round cell tumor: report of a case with elevated serum levels and prominent signet ring morphology.

Serum assays for CA 125 are often used in the diagnosis and follow-up of patients with gynecologic neoplasms. A case of a 34-year-old woman with desmoplastic small round cell tumor (DSRCT) having an unusual morphology, including the presence of a signet ring cell component, and high serum CA 125 levels that was initially diagnosed as poorly differentiated carcinoma of the ovary is herein reported. Ultrastructurally, the signet ring appearance was shown to be the result of either the presence of intracytoplasmic vacuoles or dilatation of the intercellular space. Immunoperoxidase staining showed strong reactivity for desmin, keratin, vimentin, and CA 125. Immunohistochemical studies were performed on six additional DSRCTs but only two showed focal staining for CA 125. Because the patient's CA 125 serum level decreased after she received chemotherapy and her tumor was removed, and it became elevated again when the disease recurred, it is possible that CA 125 could be used as a marker of persistent and recurrent disease in those uncommon cases of DSRCT in which there are elevated serum levels of this marker at the onset of treatment.