However, already in a study from 2003, based on the analysis of 165 microdissected renal biopsies obtained from a variety of diseases, Schmid et al. showed that GAPDH, though historically frequently used [7], displays a remarkable variety in its expression level and is thus not suitable as an RG in renal tissues, as also shown in studies on renal cell carcinoma [34, 35]. This evidence concerns the gene GAPDH and renal cell carcinoma.