GRP and chronic obstructive pulmonary disease: MLR model’s P was 0.038 while the adjusted R2 was 0.046. MNLR model’s cross validation accuracy was 74.6%. P < 0.05 was considered statistically significant. proGRP - progastrin-releasing peptide. COPD - chronic obstructive pulmonary disease. ADC - adenocarcinoma. SQCC - squamous cell carcinoma. NET - neuroendocrine tumor. CRP - C-reactive protein. NSE - neuron specific enolase. CEA - carcinoembryonic antigen. CYFRA - cytokeratin 19 fragment 21-1.