Although some authors suggest that prolidase activity decreases in some disease conditions, such as asthma [13], chronic obstructive pulmonary disease [14], and ankylosing spondylitis [15], increased prolidase activity has been reported in some other diseases and cancers (pancreatic cancer, lung carcinoma, breast cancer) [16–19]. This evidence concerns the gene PEPD and chronic obstructive pulmonary disease.