CDKN2A and lung cancer: Seven tumor suppressor genes (<i>CDKN2A</i>, <i>CDH13</i>, <i>MGMT</i>, <i>MIR137</i>, <i>DAPK1</i>, <i>RARB</i>, and <i>RASSF1A</i>) consistently exhibited hypermethylation in both lung cancer and in association with smoking exposure.