We used RNA isolated from kidney cancer samples and assessed the expression levels of the previously mentioned circRNAs and their linear counterparts, including those of the reference genes PPIA and TBP. In addition, we used prostate cancer samples and included circCSNK1G3. A circRNA deregulated in PCa 38 and the established mRNA normalizers ALAS1 and HPRT1 for PCa expression studies 44 in our assay panel. This evidence concerns the gene PPIA and kidney cancer.