In women with a history of gynecologic tumor and proliferative cells in a papillary arrangement in a metastasis, PAX8 is very helpful in that it is a highly specific marker for neoplasms originating in the Müllerian duct system [6], whereas strong WT1 positivity points toward extra-uterine serous differentiation [7]. The gene discussed is WT1; the disease is female reproductive system neoplasm.