GAPDH and lung cancer: Most lung cancer qPCR studies use commercial RGs, such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) [12], β-actin (ACTB) [13], TATA-binding protein [14], β-microglobulin [15], cytochrome oxidase II [16], 18S ribosomal RNA (rRNA18S) [4].