PAX8 is a member of the paired box (PAX) family of transcription factors,typically containing a paired box domain and a paired-type homeodomain. It is expressed during organogenesis of the thyroid gland,kidney and Mullerian system. It is thought to regulate the expression of Wilms tumor suppressor (WT1) gene and mutations in PAX8 have been associated with Wilms tumor cells,thyroid and ovarian carcinomas. PAX8 is a useful marker in distinguishing ovarian carcinomas from mammary carcinomas . PAX8 is expressed in a high percentage of ovarian serous,endometrioid,and clear cell carcinomas,but only rarely in primary ovarian mucinous adenocarcinomas. PAX8 has 5 isoforms with calculated MW 31kd,34kd,41kd,43kd and 48kd. And there is a 60kd band corresponding to the electrophoretic mobility of PAX8 .