PAX8 and clear cell adenocarcinoma: The biopsy of the lesion showed clear cell carcinoma with sarcomatoid differentiation that stained positive for SV40-BKPyV in the nuclei, with the surrounding healthy kidney tissue being negative, and positive for the sarcomatoid/clear cell markers carbonic anhydrase IX (CAIX), paired box gene 8 (PAX8), and vimentin (Figure 2).