PAX8 (Paired Box 8) is a transcription factor encoded by the *PAX8* gene, belonging to the PAX family of proteins critical during embryonic development. It plays a vital role in organogenesis, particularly in the urinary system (kidneys) and the thyroid gland, where it regulates cell differentiation and tissue-specific gene expression. In diagnostic pathology, PAX8 antibodies are widely used as immunohistochemical markers to identify tissues and tumors derived from these organs.
PAX8 expression is strongly associated with epithelial cancers, including ovarian carcinomas (e.g., serous and endometrioid subtypes), renal cell carcinomas, and thyroid carcinomas (e.g., papillary and follicular types). Its nuclear staining pattern helps distinguish these malignancies from morphologically similar tumors, aiding in differential diagnosis. For instance, PAX8 is often positive in Müllerian-origin tumors but negative in gastrointestinal or lung adenocarcinomas, making it valuable in determining the primary site of metastatic cancers.
Research also explores PAX8's role in tumorigenesis, as its dysregulation may contribute to cancer progression. While highly sensitive, PAX8 is not entirely specific; occasional expression is observed in other neoplasms (e.g., neuroendocrine tumors). Nonetheless, it remains a cornerstone in surgical pathology, often used alongside other markers (e.g., PAX2. TTF-1) to refine diagnostic accuracy. Recent studies further investigate its prognostic implications and therapeutic targeting potential.