Lubin J H, Boice J D
Epidemiology and Biostatistics Program, National Cancer Institute, Bethesda, MD, USA.
J Natl Cancer Inst. 1997 Jan 1;89(1):49-57. doi: 10.1093/jnci/89.1.49.
Studies of underground miners exposed to radioactive radon and its decay products have found that exposure increases risk of lung cancer. Consequently, when radon was found to accumulate in houses, there was concern about the public health impact from exposure to a known carcinogen. Estimates on the basis of studies of underground miners suggest that indoor radon may account for 6000-36,000 lung cancer deaths each year in the United States. Because of differences between working in underground mines and living in houses, estimates are subject to major uncertainties. Numerous case-control studies were launched to assess directly the lung cancer risk from indoor radon. Some studies report positive or weakly positive findings, while others report no increased risk. Thus, the potential hazard from indoor radon remains answered only indirectly through miner studies, experimental animal studies, and cellular studies.
To provide more information on the risk of lung cancer from indoor radon, we conducted a meta-analysis of all case-control studies that included at least 200 case subjects each and that used long-term indoor radon measurements.
Eight studies were available and included a total of 4263 lung cancer case subjects and 6612 control subjects. From the published results of each study, confounder-adjusted relative risk (RR) estimates and 95% confidence intervals (CIs) for categories of radon concentration were obtained, and weighted linear regression analyses were performed.
The combined trend in the RR was significantly different from zero (two-sided P = .03), and an estimated RR of 1.14 (95% CI = 1.0-1.3) at 150 Bq/m3 was found. An influence analysis indicated that no single study dominated the combined results. The exposure-response trend was similar to model-based extrapolations from miners and to RRs computed directly from miners with low cumulative exposures. However, there were significant differences in the study-specific estimates of the exposure response (two-sided P < .001), which were not explained by study differences in percent of the defined exposure interval covered by radon measurements, mean number of residences per subject, and other factors.
Meta-analyses are valuable for identifying differences among studies and for summarizing results, but they should be interpreted cautiously when expected RRs are low as with indoor radon exposure, when there is study heterogeneity and where there is the potential for confounding and exposure misclassification. Nonetheless, the results of this meta-analysis suggest that the risk from indoor radon is not likely to be markedly greater than that predicted from miners and indicate that the negative exposure response reported in some ecologic studies is likely due to model misspecification or uncontrolled confounding and can be rejected.
Until ongoing case-control studies of indoor radon are completed and the data are pooled and analyzed, the studies of underground miners remain the best source of data to use to assess risk from indoor radon. This meta-analysis provides support for their general validity.
对接触放射性氡及其衰变产物的地下矿工的研究发现，接触会增加患肺癌的风险。因此，当发现氡在房屋中积聚时，人们担心接触已知致癌物会对公众健康产生影响。根据对地下矿工的研究估计，在美国，室内氡每年可能导致6000 - 36000例肺癌死亡。由于在地下矿井工作和在房屋中生活存在差异，这些估计存在很大的不确定性。开展了大量病例对照研究以直接评估室内氡导致肺癌的风险。一些研究报告了阳性或弱阳性结果，而其他研究则报告没有增加风险。因此，室内氡的潜在危害仍然只能通过矿工研究、实验动物研究和细胞研究间接得到解答。
为了提供更多关于室内氡导致肺癌风险的信息，我们对所有至少包含200例病例且使用长期室内氡测量的病例对照研究进行了荟萃分析。
有八项研究可供使用，共纳入4263例肺癌病例和6612例对照。从每项研究的已发表结果中，获取了经混杂因素调整的相对风险（RR）估计值以及氡浓度类别的95%置信区间（CI），并进行了加权线性回归分析。
RR的综合趋势与零有显著差异（双侧P = 0.03），在150 Bq/m³时估计的RR为1.14（95% CI = 1.0 - 1.3）。影响分析表明，没有一项研究主导综合结果。暴露 - 反应趋势与基于矿工的模型外推以及直接从累积暴露量低的矿工计算出的RR相似。然而，各研究中暴露反应的估计值存在显著差异（双侧P < 0.001），这些差异无法通过氡测量覆盖的定义暴露区间百分比、每个受试者的平均居住次数及其他因素的研究差异来解释。
荟萃分析对于识别研究之间的差异和总结结果很有价值，但当预期RR较低（如室内氡暴露）、存在研究异质性以及存在混杂和暴露错误分类的可能性时，应谨慎解释。尽管如此，该荟萃分析的结果表明，室内氡的风险不太可能明显高于从矿工研究中预测的风险，并表明一些生态学研究中报告的负暴露反应可能是由于模型设定错误或未控制的混杂因素导致的，并且可以被否定。
在正在进行的室内氡病例对照研究完成并汇总分析数据之前，地下矿工的研究仍然是评估室内氡风险的最佳数据来源。这项荟萃分析为其总体有效性提供了支持。
