CDKN2A and neoplasm: &lt;i&gt;CDKN2A&lt;/i&gt;/&lt;i&gt;p16&lt;/i&gt; Exon 2 Hypermethylation in Lung Squamous Cell Carcinoma Associated with Interstitial and Emphysematous Lung Diseases: A Comparative Analysis of Tumor, Adjacent and Distant Lung Tissues.