Interactions between CagA and smoking in gastric cancer

Table 1 Basic characteristics of cases and controls

Demographic data	Cases (n = 257)	Control (n = 514)	χ2	P
Race
Chinese Han	240	469	1.061	0.303
Others	17	45
Education level (yr)
< 6	82	175	2.075	0.557
6-9	87	155
9-12	47	110
> 12	41	74
BMI (kg/m2)
≤ 25	172	374	2.824	0.093
> 25	85	140

BMI: Body nass index.

Table 2 Smoking habits of cases and controls

	Cases (n = 257)	Control (n = 514)
Non-smoker (%)	90 (35)	355 (69)
Current smoker (%)	69 (27)	56 (11)
Former smoker (%)	98 (38)	103 (20)
Smoker (%)	167 (65)	159 (31)
Age of starting smoking	19 (15-20)	18 (15-20.5)
Cigarettes/d	21 (15-27)	22 (10-30)
Pack/yr	28 (16-42)	25 (10-39)

Data represent means, with interquartile ranges in parentheses.

Table 3 Odds ratios of CagA positive Helicobacter pylori infection and smoking in non-cardiac cancer n (%)

	Cases (n = 257)	Control (n = 514)	Crude		Adjusted
			OR	95% CI	OR	95% CI
CagA
Tertile 1	45 (17.5)	249 (48.5)	1.0		1.0
Tertile 2	85 (33.0)	170 (33.0)	2.3	1.2-3.9	3.8	1.4-7.2
Tertile 3	127 (49.5)	95 (18.5)	4.1	2.7-6.3	12.41	6.1-20.3
P value				0		0.003
Smoking status
Never smoked	90 (35.0)	355 (69.0)	1.0		1.0
Smoking	167 (65.0)	159 (31.0)	3.6a	2.5-5.3	5.42a	2.3-9.0

^aP < 0.05.

¹Adjusted for education, alcohol consumption, smoking and family history of gastric cancer;

²Adjusted for education, alcohol consumption, family history of gastric cancer and Helicobacter pylori infection. CagA: Cytotoxin-associated gene; OR: Odds ratio.

Table 4 Risk and synergy index¹ of non-cardia gastric cancer according to CagA positive Helicobacter pylori infection and smoking n (%)

	Cases(n = 257)	Control(n = 514)	Crude		Adjusted2		SF	SF (95% CI)	Z	P
			OR	95% CI	OR	95% CI
Smoking status							2.257	1.133-4.496	2.315	0.021a
CagA (-) and never smoked	30 (11.7)	269 (52.4)	1.0		1.0
CagA (-) and smoking	45 (17.5)	105 (20.4)	3.5	1.9-5.1	2.7	1.3-4.9
CagA (+) and never smoked	60 (23.3)	85 (16.5)	3.5	1.8-5.3	3.2	1.5-6.8
CagA (+) and smoking	122 (47.5)	55 (10.7)	8.7	5.1-11.9	19.5	10.3-42.2

^aP < 0.05. ¹Synergy index, is the ratio of the observed odds ratio (OR) for both factors combined, to the predicted OR assuming independent effects of each factor;

²Adjusted for education, alcohol consumption and family history of gastric cancer.