PAX-8 is a transcription factor that is active during the embryonic formation of Müllerian structures, kidneys, and the thyroid. Its expression continues in certain epithelial cell types of these fully developed organs. PAX-8 serves as an important marker for tumors that originate from gynecological, renal, and thyroid sources.

The PAX-8 (MRQ-50) antibody focuses on the N-terminal portion of the PAX-8 protein. This part of the molecule is also found in other PAX proteins like PAX-5 and PAX-6, leading to some potential cross-reactivity with these proteins. This is demonstrated by the labeling of specific lymphocytes and neuroendocrine cells.