CDKN1A and chronic obstructive pulmonary disease: However, tumor expression of its downstream markers SNAIL-1 and P53 was significantly lower in LC-COPD than LC patients, while that of CDKN2A was greater and that of P63, CDKN1A, and ki-67 did not differ in tumors between patient groups (Table 2 and Additional file 1: Figure S3).