Radon epidemiology: continuous and categorical trend estimators when the exposure distribution is skewed and outliers may be present

As other epidemiological exposure variables, indoor radon levels have a right-skewed, approximately lognormal distribution. The continuous linear trend estimator is then known to be sensitive to outlying observations. We consider trend estimators based on replacing the exposure x by a transformed variable z: (1) trimmed estimators, that is, extreme values are deleted in z; (2) winsorized estimators, that is, extreme values are replaced by a lower value; (3) categorical estimators, that is, x is categorized and the continuous variable z takes on scores such as the mean or median within categories. The latter approach is often used in meta-analyses of published odds ratios. Statistically optimal categories can be defined. The corresponding scores are the expected values within the categories, based on the assumption of a lognormal distribution. In a simulation study, it turned out that procedures with different cutpoints for cases and controls, winsorized estimators, and categorical estimators based on category medians can be badly biased upward. Categorical estimators using category means are not always robust against outlying observations. However, categorical estimators employing optimal categories with expected values are nearly unbiased, even in the presence of outliers. Cutpoints should be determined according to the overall distribution of cases and controls combined. Trimmed estimators based on this distribution are unbiased, but highly variable. For right-skewed exposure variables, we therefore suggest sensitivity analyses based on the categorical estimator with optimal cutpoints and expected value scores. In the West German case-control study on indoor radon and lung cancer, these sensitivity analyses lead to increased risk estimates.

Lung cancer risk among former uranium miners of the WISMUT Company in Germany

After 1946, the WISMUT Company developed the third-largest uranium-mining province in the world in the German Democratic Republic.

METHODS

A case-control study among former WISMUT miners was conducted to investigate the lung cancer risk in relation to attained age, time since exposure, exposure duration, and exposure rate. It consisted of 505 patients with lung cancer and 1,073 controls matched to cases according to the year of birth. The cumulative exposure to radon and radon decay products was calculated as the sum of yearly exposures and expressed in Working Level Months (WLM). Cases had a mean cumulative exposure of 552 WLM compared to 420 WLM in controls.

RESULTS

There was a statistically significant increase in lung cancer risk for cumulative exposures above 800 WLM. Under the assumption of a linear risk model, there was a significant increase in the relative risk of 0.10 per 100 WLM after adjusting for smoking and asbestos exposure. For current smokers the increase in relative risk was lower (0.05 per 100 WLM), whereas it was higher (0.20 per 100 WLM) among nonsmokers and longtime ex-smokers. After correcting in a sensitivity analysis for the fact that the controls of this study had a higher average exposure than the population of WISMUT workers they were recruited from, the adjusted ERR increased to 0.24 per 100 WLM. Lung cancer risk declined with time since exposure, except for exposures received 45 or more years ago. No inverse dose rate effect was observed.

Residential radon and lung cancer--detailed results of a collaborative analysis of individual data on 7148 persons with lung cancer and 14,208 persons without lung cancer from 13 epidemiologic studies in Europe

OBJECTIVES

Studies seeking direct estimates of the lung cancer risk associated with residential radon exposure lasting several decades have been conducted in many European countries. Individually these studies have not been large enough to assess moderate risks reliably. Therefore data from all 13 European studies of residential radon and lung cancer satisfying certain prespecified criteria have been brought together and analyzed.

METHODS

Data were available for 7148 persons with lung cancer and 14,208 controls, all with individual smoking histories and residential radon histories determined by long-term radon gas measurements.

RESULTS

The excess relative risk of lung cancer per 100 Bq/m3 increase in the observed radon concentration was 0.08 [95% confidence interval (95% CI) 0.03-0.16; P=0.0007] after control for confounding. The dose-response relationship was linear with no evidence of a threshold, and it remained significant when only persons with observed radon concentrations of <200 Bq/m3 were included. There was no evidence that the excess relative risk varied with age, sex, or smoking history. Removing the bias induced by random uncertainties related to radon exposure assessment increased the excess relative risk of lung cancer to 0.16 (95% CI 0.05-0.31) per 100 Bq/m3. With this correction, estimated risks at 0, 100, and 400 Bq/m3, relative to lifelong nonsmokers with no radon exposure, were 1.0, 1.2, and 1.6 for lifelong nonsmokers and 25.8, 29.9, and 42.3 for continuing smokers of 15-24 cigarettes/day.

CONCLUSIONS

These data provide firm evidence that residential radon acts as a cause of lung cancer in the general population. They provide a solid basis for the formulation of policies with which to manage risk from radon and reduce deaths from the most common fatal cancer in Europe.

Increased lung cancer risk due to residential radon in a pooled and extended analysis of studies in Germany

Residential radon has been shown to be a risk factor for lung cancer in several studies-but with limited power in each single study. The data of two case-control studies performed during 1990-1997 in Germany and used for previous publications have been extended and pooled. Both studies have identical study designs. In total, data of 2,963 incident lung cancer cases and 4,232 population controls are analyzed here. One-year radon measurements were performed in houses occupied during the 5-35 y prior to the interview. Conditional logistic and linear relative risk regression was used for the analysis. Measurements covered on average 70% of the exposure time window, with an average radon exposure of 61 Bq m(-3). The smoking and asbestos-adjusted ORs were 0.97 [95% confidence interval (CI) 0.85 to 1.11] for 50-80 Bq m(-3), 1.06 (95% CI 0.87 to 1.30) for 80-140 Bq m(-3) and 1.40 (95% CI 1.03 to 1.89) for radon concentrations above 140 Bq m(-3), compared to the reference category <50 Bq m(-3). The linear increase in the odds ratio per 100 Bq m(-3) was 0.10 (95% CI -0.02 to 0.30) for all subjects and 0.14 (95% CI -0.03 to 0.55) for less mobile subjects who lived in only one home in the last 5-35 y. The risk coefficients generally were higher when measurement error in the radon concentrations was reduced by restricting the population. With respect to histopathology, the risk for small cell carcinoma was higher than for other subtypes. This analysis strengthens the evidence that residential radon is a relevant risk factor for lung cancer.

Residential radon and risk of lung cancer in Eastern Germany

BACKGROUND

There is suggestive evidence that residential radon increases lung cancer risk. To elucidate this association further, we conducted a case-control study in Thuringia and Saxony in Eastern Germany during 1990-1997.

METHODS

Histologically confirmed lung cancer patients from hospitals and a random sample of population controls matched on age, sex and geographical area were personally interviewed with respect to residential history, smoking, and other risk factors. One-year radon measurements were performed in houses occupied during the 5-35 years prior to the interview. The final analysis included a total of 1,192 cases and 1,640 controls. Odds ratios (OR) and 95% confidence intervals (CI) were estimated by logistic regression.

RESULTS

Measurements covered on average 72% of the exposure time window, with mean radon concentrations of 76 Bq/m3 among the cases and 74 Bq/m3 among the controls. The smoking- and asbestos-adjusted ORs for categories of radon (50-80, 80-140 and >140 Bq/m*3, compared with 0-50 Bq/m3) were 0.95 (CI = 0.77 to 1.18), 1.13 (CI = 0.86 to1.50) and 1.30 (CI = 0.88 to 1.93). The excess relative risk per 100 Bq/mł was 0.08 (CI = -0.03 to 0.20) for all subjects and 0.09 (CI = -0.06 to 0.27) for subjects with complete measurements for all 30 years.

CONCLUSIONS

Our data indicate a small increase in lung cancer risk as a result of residential radon that is consistent with the findings of previous indoor radon and miner studies.

Risk factors for lung cancer among nonsmoking women

To evaluate risk factors for lung cancer in nonsmoking women, we used data of a case-control study conducted between 1991 and 1996 in Germany. A total of 234 female histologically confirmed lung cancer patients and 535 population controls who had never smoked more than 400 cigarettes in their lifetime were personally interviewed with respect to occupation, exposure to environmental tobacco smoke (ETS), family history of cancer, prior physician-diagnosed lung diseases or cancer and diet. One-year radon measurements in the last dwelling were performed. Odds ratios (OR) adjusted for age and region and 95% confidence intervals (CI) were calculated via logistic regression. When cumulative duration of exposure to ETS in hours was considered, the OR for high compared to not or low ETS exposed women was 2.62 (CI:1.35-5.06) for occupational exposure and OR=1.67 (CI:0.86-3.25) for spousal exposure, exhibiting a significant trend for ETS at work. Working more than 10 years in jobs or industries with known or suspected lung carcinogens was associated with OR=2.0 (CI:0.99-4.0). An elevated risk due to prior lung diseases was present for pneumonia (OR=1.6; CI:1.07-2.40) and tuberculosis (OR=1.6; CI:0.77-3.37). No significant increase in risk with increasing residential radon levels or with the presence of a family history of lung cancer was apparent. Protective effects were observed for high vs. low consumption of fresh vegetables (OR=0.5; CI:0.25-0.82) and cheese (OR=0.3, CI:0.21-0.55). ETS at work, occupational hazards and previous pneumonia may be risk factors for lung cancer in nonsmoking women, while a diet rich in fresh vegetables and cheese seems to be protective.