WT1 and oncocytic adenoma: The first and only other dedicated investigation, undergone over 20 years ago, on the topic of constitutive expression of WT1 in aRCCs used cell cultures (five ccRCCs and one oncocytoma) and demonstrated that four out of five ccRCCs and the only oncocytoma tested expressed measurable WT1 RNA, at levels less than those observed in the human fetal kidney cultures (included for comparison), but significantly higher than those seen in cultured proximal tubular epithelial cells.