MMP12 and chronic obstructive pulmonary disease: There were no changes in tumor numbers and inflammatory cell infiltration of NTHi exposed CC-LR-NEKO mice (Additional file 3: Figure S3A, and S3B), suggesting roles for other recruited inflammatory cells, such as macrophages and their products (e.g. macrophage elastase) in promotion of lung cancer by COPD-type airway inflammation.