SOX9 and neoplasm: The embryonic sex cords derive from the coelomic epithelium13; therefore, as a general concept, tumours with a sex cord phenotype (e.g., Sertoli cell tumours) typically express some of the markers that are also positive in mesothelial cells (e.g., WT1) as well as transcription factors associated with differentiation of primitive sex cord cells to Sertoli and granulosa cells (e.g., SOX9 and FOXL2, respectively).14, 15