Overview of the study characteristics
A flowchart depicting the study selection process is shown in Figure 1. In total, 746 articles were selected on the basis of various combinations of the keywords listed in the “Methods and materials” section. Checking for duplicates resulted in the removal of 660 articles. Of the remaining 86 articles, 65 were excluded for the following reasons: lack of relevance, since the articles did not explore the association between XRCC1 SNPs and leukemia risk (n=23); did not focus on susceptibility to leukemia (n=24); were review articles (n=13); or provided insufficient data (n=5). Thus, only 21 articles qualified for inclusion in this meta-analysis, among which 5, 10, 3, 2, and 1 focused on AML,3,9–12 ALL,13–22 CLL,23–25 CML,26,27 and both AML and CML,28 respectively.
Basic data for every eligible study were extracted and are listed in Table 1. In one article,16 in which different ethnic populations were evaluated, data for each ethnicity were collected separately and were treated in the present analysis as independent studies. Moreover, another included article28provided separate data for two types of leukemia; further, data for each leukemia type were analyzed as if they were from different studies. As a result, data from a final total of 23 studies were finally included in this meta-analysis. However, the genetic distributions of the control groups did not conform with HWE in three of these studies,10,11,27 which were thus excluded from the meta-analysis. The distribution of the remaining studies regarding meta-analysis of the association between XRCC1Arg399Gln SNP and risk of each type of leukemia was as follows: ALL, eleven studies (1,088 cases and 1,588 controls); AML, four studies (345 cases and 651 controls); CML, two studies (338 cases and 406 controls); and CLL, three studies (712 cases and 614 controls).
(To view a larger version of Table 1, click here.)
Table 2 lists the main results of the meta-analysis. The findings are discussed for each leukemia type separately in the following section.
(To view a larger version of Table 2, click here.)