We isolated and cultured primary cells from p16+/−;Brca1MGKO mammary tumors and found that p16 mRNA levels were significantly increased in the 1347 tumor cells treated with 5-aza-2′-deoxycytidine (DAC), a methylation inhibitor, but not in the 1255 tumor cells (Figure 4D), confirming the findings derived by MS-PCR in tumors. The gene discussed is CDKN2A; the disease is breast cancer.