Examination of lung tissue sections from patients who were undergoing lung lobectomy for peripheral carcinoma showed that smokers with COPD, the percentage of YKL-40 positive cells (27.1 [21.9–34.2]%) was significantly increased than those without COPD (16.8 [13.9–20.8]%; p = 0.002) and non-smokers (14.2 [9.4–17.9]%; p < 0.001) (Fig. 2a–c, e). The gene discussed is CHI3L1; the disease is chronic obstructive pulmonary disease.