Histologically, it had a papillary architecture mimicking ovarian serous carcinoma and was immunopositive for paired box gene 8 (PAX8), vimentin, P504S, P53, and CK20 (focal) and negative for CK7, WT-1, high molecular weight cytokeratin and p63, CK5/6, CD10, and estrogen receptors, supporting the diagnosis of RCCU. This evidence concerns the gene PAX8 and ovarian serous carcinoma.