Table 1. The baseline characteristics of study population.

Characteristics	Patients (n = 819)	Controls (n = 803)	P**
Age (years)	57.35 (10.51)	57.04 (9.72)	0.846
Sex (male)	64.84%	64.76%	0.974
Smokers	36.26%	7.97%	<0.0005
Drinkers	16.85%	8.09%	<0.0005
COPD history	14.53%	4.73%	<0.0005
Family history of cancers	11.36%	10.83	0.738
Lung cancer subtypes
Squamous cell cancer	36.16%	−*
Adenocarcinoma	31.75%	−
Small cell cancer	19.79%	−
Others	12.3%

Abbreviations: COPD, chronic obstructive pulmonary disease. Data are expressed as mean (standard deviation or SD) or percentage as indicated.

^*data not available.

^**P values were calculated by using unpaired t-test for age, and by χ2 test for other categorical characteristics.