Thus, in BKPyV-associated malignancies, the positive immunoreaction for PAX8, pan-cytokeratins, CK7 and vimentin and the negative immunoreaction for EMA, CK20, GATA3, p504S, S100, HMB45 and CD45 certify the renal or urothelial cell origin of the tumor [18,24,80]; supplementarily, the positive expression of E-cadherin, INI1 and CA9 differentiates a rare variant of RCC, namely, collecting duct carcinoma [80]. The gene discussed is SMARCB1; the disease is collecting duct carcinoma.