The Arg399Gln polymorphism was associated with a significant decreased risk [allelic contrast: OR = 0.73, 95% CI = 0.59-0.92, P(Z) = 0.006, P(Q) = 0.31; dominant model: OR = 0.73, 95% CI = 0.55-0.97, P(Z) = 0.03, P(Q) = 0.33; recessive model: OR = 0.56, 95% CI = 0.34-0.93, P(Z) = 0.02, P(Q) = 0.59], while the Arg194Trp SNP conferred an increased risk for thyroid cancer in the mixed populations [allelic contrast: OR = 1.49, 95% CI = 1.02-2.17, P(Z) = 0.04].
Overall, no significant association was found between XRCC1 Arg399Gln (recessive model: OR = 0.95, 95% CI = 0.77-1.15; dominant model: OR = 0.89, 95% CI = 0.75-1.05; homozygote model: OR = 0.92, 95% CI = 0.69-1.23; Heterozygote model: OR = 0.91, 95% CI = 0.80-1.03; additive model: OR = 0.93, 95% CI = 0.81-1.07), Arg194Trp (recessive model: OR = 1.41, 95% CI = 0.62-3.23; dominant model: OR = 1.01, 95% CI = 0.77-1.34; homozygote model: OR = 1.42, 95% CI = 0.55-3.67; Heterozygote model: OR = 1.03, 95% CI = 0.85-1.26; additive model: OR = 1.08, 95% CI = 0.81-1.42), and Arg280His (recessive model: OR = 1.08, 95% CI = 0.56-2.10; dominant model: OR = 1.01, 95% CI = 0.84-1.22; homozygote model: OR = 1.00, 95% CI = 0.51-1.96; Heterozygote model: OR = 1.04, 95% CI =0.75-1.42; additive model: OR = 1.03, 95% CI = 0.86-1.23) and thyroid cancer risk when all the eligible studies were pooled into the meta-analysis.
However, subgroup analysis revealed: 1) an elevated risk in aa vs AA analysis (OR=2.03, 95%CI= 1.24-3.31) and recessive genetic model analysis (OR=1.93, 95%CI= 1.20-3.08) in the larger sample size trials for XRCC1 Arg194Trp polymorphism; 2) a decreased thyroid cancer risk on subgroup analysis based on ethnicity in Aa vs AA analysis (OR=0.84, 95%CI= 0.72-0.98) and in a dominant genetic model (OR=0.84, 95%CI= 0.72-0.97) in Caucasian populations for the XRCC1 Arg399Gln polymorphism; 3) a decreased thyroid cancer risk on subgroup analysis based on design type in Aa vs AA analysis (OR=0.72, 95% CI= 0.54-0.97) among the PCC trials for the Arg399Gln polymorphism.