Diagnosis: Pax-8 immunohistochemistry
• PAX-8 is a transcription factor involved in the organogenesis of multiple organs, including the thyroid, kidney, and mullerian system.
• PAX-8 is a useful immunohistochemical marker, particularly in the setting of metastatic disease. In the kidney, it is expressed in all renal cell carcinoma subtypes and is, thus, of no utility in subclassifying renal cell carcinoma; however, when limited material is available or a poorly differentiated carcinoma is present, it is useful in distinguishing renal cell carcinoma from urothelial carcinoma.
• In addition, it is helpful in distinguishing renal cell carcinoma from its mimickers, adrenocortical carcinoma and heptocellular carcinoma. Similar to most other immunohistochemical markers, it is most useful when used as part of a panel of immunohistochemical stains.
