CDKN2A and breast carcinoma: To determine if this was the case in breast cancer, DNA was isolated from 25 breast tumors (12 from women with the CG genotype and 13 with the CC genotype), and multiplex PCR used to estimate the gene dosage of CDKN2A exon 1a (p16INK4a) and exon 1b (p14ARF) relative to an internal beta-globin gene fragment (29).