Reliability, stability during long-term storage, and intra-individual variation of circulating levels of osteopontin, osteoprotegerin, vascular endothelial growth factor-A, and interleukin-17A

BACKGROUND

Studies in many populations have reported associations between circulating cytokine levels and various physiological or pathological conditions. However, the reliability of cytokine measurements in population studies, which measure cytokines in multiple assays over a prolonged period, has not been adequately examined; nor has stability during sample storage or intra-individual variation been assessed.

METHODS

We assessed (1) analytical reliability in short- and long-term repeated measurements; (2) stability and analytical reliability during long-term sample storage, and (3) variability within individuals over seasons, of four cytokines-osteopontin (OPN), osteoprotegerin (OPG), vascular endothelial growth factor-A (VEGF-A), and interleukin-17A (IL-17A). Measurements in plasma or serum samples were made with commercial kits according to standard procedures. Estimation was performed by fitting a random or mixed effects linear model on the log scale.

RESULTS

In repeated assays over a short period, OPN, OPG, and VEGF-A had acceptable reliability, with intra- and inter-assay coefficients of variation (CV) less than 0.11. Reliability of IL-17A was poor, with inter- and intra-assay CV 0.85 and 0.43, respectively. During long-term storage, OPG significantly decayed (- 33% per year; 95% confidence interval [- 54, - 3.7]), but not OPN or VEGF-A (- 0.3% or - 6.3% per year, respectively). Intra- and inter-assay CV over a long period were comparable to that in a short period except for a slight increase in inter-assay CV of VEGF-A. Within-individual variation was small for OPN and VEGF-A, with intra-class correlations (ICC) 0.68 and 0.83, respectively, but large for OPG (ICC 0.11).

CONCLUSIONS

We conclude that OPN and VEGF-A can be reliably measured in a large population, that IL-17A is suitable only for small experiments, and that OPG should be assessed with caution due to degradation during storage and intra-individual variation. The overall results of our study illustrate the need for validation under relevant conditions when measuring circulating cytokines in population studies.

Candidate biomarkers and persistent transcriptional responses after low and high dose ionizing radiation at high dose rate

PURPOSE

Development of an integrated time and dose model to explore the dynamics of gene expression alterations and identify biomarkers for biodosimetry following low- and high-dose irradiations at high dose rate.

MATERIAL AND METHODS

We utilized multiple transcriptome datasets (GSE8917, GSE43151, and GSE23515) from Gene Expression Omnibus (GEO) for identifying candidate biological dosimeters. A linear mixed-effects model with random intercept was used to explore the dose-time dynamics of transcriptional responses and to functionally characterize the time- and dose-dependent changes in gene expression.

RESULTS

We identified genes that are correlated with dose and time and discovered two clusters of genes that are either positively or negatively correlated with both dose and time based on the parameters of the model. Genes in these two clusters may have persistent transcriptional alterations. Twelve potential transcriptional markers for dosimetry-ARHGEF3, BAX, BBC3, CCDC109B, DCP1B, DDB2, F11R, GADD45A, GSS, PLK3, TNFRSF10B, and XPC were identified. Of these genes, BAX, GSS, and TNFRSF10B are positively associated with both dose and time course, have a persistent transcriptional response, and might be better biological dosimeters.

CONCLUSIONS

With the proposed approach, we may identify candidate biomarkers that change monotonically in relation to dose, have a persistent transcriptional response, and are reliable over a wide dose range.

Translocations are induced in hematopoietic stem cells after irradiation of fetal mice

Although mammalian fetuses have been suggested to be sensitive to radiation, an increased frequency of translocations was not observed in blood lymphocytes from atomic bomb (A-bomb) survivors who were exposed to the bomb in utero and examined as adults. Since experiments using hematopoietic cells of mice and rats confirmed this finding, it was hypothesized that either irradiated fetal hematopoietic stem cells (f-HSCs) cannot generate exchange-type chromosomal aberrations or cells bearing induced aberrations are eliminated before the animals reach adulthood. In the present study, pregnant mice (12.5-15.5 days post coitum [dpc]) were irradiated with 2 Gy of X-rays and long-term HSCs (LT-HSCs) were isolated 24 h later. Multicolor fluorescence in situ hybridization (mFISH) analysis of LT-HSC clones proliferated in vitro showed that nine out of 43 (21%) clones from fetuses and 21 out of 41 (51%) clones from mothers bore translocations. These results indicate that cells with translocations can arise in mouse f-HSCs but exist at a lower frequency than in the mothers 24 h after X-ray exposure. Thus, it seems likely that translocation-bearing f-HSCs are generated but subsequently disappear, so that the frequency of lymphocyte translocations may decrease and reach the control level by the time the animals reach adulthood.

Age effects on radiation response: summary of a recent symposium and future perspectives

One of the principal uncertainties when estimating population risk of late effects from epidemiological data is that few radiation-exposed cohorts have been followed up to extinction. Therefore, the relative risk model has often been used to estimate radiation-associated risk and to extrapolate risk to the end of life. Epidemiological studies provide evidence that children are generally at higher risk of cancer induction than adults for a given radiation dose. However, the strength of evidence varies by cancer site and questions remain about site-specific age at exposure patterns. For solid cancers, there is a large body of evidence that excess relative risk (ERR) diminishes with increasing age at exposure. This pattern of risk is observed in the Life Span Study (LSS) as well as in other radiation-exposed populations for overall solid cancer incidence and mortality and for most site-specific solid cancers. However, there are some disparities by endpoint in the degree of variation of ERR with exposure age, with some sites (e.g., colon, lung) in the LSS incidence data showing no variation, or even increasing ERR with increasing age at exposure. The pattern of variation of excess absolute risk (EAR) with age at exposure is often similar, with EAR for solid cancers or solid cancer mortality decreasing with increasing age at exposure in the LSS. We shall review the human data from the Japanese LSS cohort, and a variety of other epidemiological data sets, including a review of types of medical diagnostic exposures, also some radiobiological animal data, all bearing on the issue of variations of radiation late-effects risk with age at exposure and with attained age. The paper includes a summary of several oral presentations given in a Symposium on "Age effects on radiation response" as part of the 67th Annual Meeting of the Radiation Research Society, held virtually on 3-6 October 2021.

Chromosome aberrations among atomic-bomb survivors exposed in utero: updated analysis accounting for revised radiation doses and smoking

A previous study of peripheral blood lymphocyte translocations around age 40 among atomic-bomb survivors exposed in utero revealed no overall association with radiation dose-despite a clear association between translocations and dose among their mothers-but the data suggested an increase at doses below 100 mGy with a definite peak. That analysis of the in utero-exposed survivors did not adjust for their subsequent smoking behavior, an established cause of chromosomal aberrations, or their subsequent exposures to medical irradiation, a potential mediator. In addition, atomic-bomb survivor radiation dose estimates have subsequently been updated and refined. We therefore re-estimated the dose response using the latest DS02R1 dose estimates and adjusting for smoking as well as for city and proximal-distal location at the time of exposure to the atomic bomb. Sex of the survivor, mother's age around the time of conception, and approximate trimester of gestation at the time of exposure were also considered as explanatory variables and modifiers. Precision of the estimated dose response was slightly lower due to greater variability near zero in the updated dose estimates, but there was little change in evidence of a low-dose increase and still no suggestion of an overall increase across the entire dose range. Adjustment for smoking behavior led to a decline in background number of translocations (the dose-response intercept), but smoking did not interact with dose overall (across the entire dose range). Adjustment for medical irradiation did not alter the association between dose and translocation frequency. Sex, mother's age, and trimester were not associated with number of translocations, nor did they interact with dose overall. Interactions with dose in the low-dose range could not be evaluated because of numerical instability.

Comparison of All Solid Cancer Mortality and Incidence Dose-Response in the Life Span Study of Atomic Bomb Survivors, 1958-2009

Recent analysis of all solid cancer incidence (1958-2009) in the Life Span Study (LSS) revealed evidence of upward curvature in the radiation dose response among males but not females. Upward curvature in sex-averaged excess relative risk (ERR) for all solid cancer mortality (1950-2003) was also observed in the 0-2 Gy dose range. As reasons for non-linearity in the LSS are not completely understood, we conducted dose-response analyses for all solid cancer mortality and incidence applying similar methods [1958-2009 follow-up, DS02R1 doses, including subjects not-in-city (NIC) at the time of the bombing] and statistical models. Incident cancers were ascertained from Hiroshima and Nagasaki cancer registries, while cause of death was ascertained from death certificates throughout Japan. The study included 105,444 LSS subjects who were alive and not known to have cancer before January 1, 1958 (80,205 with dose estimates and 25,239 NIC subjects). Between 1958 and 2009, there were 3.1 million person-years (PY) and 22,538 solid cancers for incidence analysis and 3.8 million PY and 15,419 solid cancer deaths for mortality analysis. We fitted sex-specific ERR models adjusted for smoking to both types of data. Over the entire range of doses, solid cancer mortality dose-response exhibited a borderline significant upward curvature among males (P = 0.062) and significant upward curvature among females (P = 0.010); for solid cancer incidence, as before, we found a significant upward curvature among males (P = 0.001) but not among females (P = 0.624). The sex difference in magnitude of dose-response curvature was statistically significant for cancer incidence (P = 0.017) but not for cancer mortality (P = 0.781). The results of analyses in the 0-2 Gy range and restricted lower dose ranges generally supported inferences made about the sex-specific dose-response shape over the entire range of doses for each outcome. Patterns of sex-specific curvature by calendar period (1958-1987 vs. 1988-2009) and age at exposure (0-19 vs. 20-83) varied between mortality and incidence data, particularly among females, although for each outcome there was an indication of curvature among 0-19-year-old male survivors in both calendar periods and among 0-19-year-old female survivors in the recent period. Collectively, our findings indicate that the upward curvature in all solid cancer dose response in the LSS is neither specific to males nor to incidence data; its evidence appears to depend on the composition of sites comprising all solid cancer group and age at exposure or time. Further follow up and site-specific analyses of cancer mortality and incidence will be important to confirm the emerging trend in dose-response curvature among young survivors and unveil the contributing factors and sites.

Radiation effects on atherosclerosis in atomic bomb survivors: a cross-sectional study using structural equation modeling

Past reports indicated that total-body irradiation at low to moderate doses could be responsible for cardiovascular disease risks, but the mechanism remains unclear. The purpose of this study was to investigate the association between radiation exposure and atherosclerosis, an underlying pathology of cardiovascular diseases, in the Japanese atomic bomb survivors. We performed a cross-sectional study measuring 14 clinical-physiological atherosclerosis indicators during clinical exams from 2010 to 2014 in 3274 participants of the Adult Health Study cohort. Multivariable analyses were performed by using a structural equation model with latent factors representing underlying atherosclerotic pathologies: (1) arterial stiffness, (2) calcification, and (3) plaque　as measured with indicators chosen a priori on the basis of clinical-physiological knowledge. Radiation was linearly associated with calcification (standardized coefficient per Gy 0.15, 95 % confidence interval: CI [0.070, 0.23]) and plaque (0.11, 95 % CI [0.029, 0.20]), small associations that were comparable to about 2 years of aging per Gy of radiation exposure, but not with arterial stiffness (0.036, 95 % CI [− 0.025, 0.095]). The model fitted better and had narrower confidence intervals than separate ordinary regression models explaining individual indicators independently. The associations were less evident when the dose range was restricted to a maximum of 2 or 1 Gy. By combining individual clinical-physiological indicators that are correlated because of common, underlying atherosclerotic pathologies, we found a small, but significant association of radiation with atherosclerosis.

Misclassification of primary liver cancer in the Life Span Study of atomic bomb survivors

Primary liver cancer is difficult to diagnose accurately at death, due to metastases from nearby organs and to concomitant diseases, such as chronic hepatitis and cirrhosis. Trends in diagnostic accuracy could affect radiation risk estimates for incident liver cancer by altering background rates or by impacting risk modification by sex and age. We quantified the potential impact of death-certificate inaccuracies on radiation risk estimates for liver cancer in the Life Span Study of atomic bomb survivors. True-positive and false-negative rates were obtained from a previous study that compared death-certificate causes of death with those based on pathological review, from 1958 to 1987. We assumed various scenarios for misclassification rates after 1987. We obtained estimated true positives and estimated false negatives by stratified sampling from binomial distributions with probabilities given by the true-positive and false-negative rates, respectively. Poisson regression methods were applied to highly stratified person-year tables of corrected case counts and accrued person years. During the study period (1958-2009), there were 1,885 cases of liver cancer, which included 383 death-certificate-only (DCO) cases; 1,283 cases with chronic liver disease as the underlying cause of death; and 150 DCO cases of pancreatic cancer among 105,444 study participants. Across the range of scenarios considered, radiation risk estimates based on corrected case counts were attenuated, on average, by 13-30%. Our results indicated that radiation risk estimates for liver cancer were potentially sensitive to death-certificate inaccuracies. Additional data are needed to inform misclassification rates in recent years.

Association Between Prevalence of Peripheral Artery Disease and Radiation Exposure in the Atomic Bomb Survivors

Background

Past reports suggested that total‐body irradiation at 0.5 to 1.0 Gy could be responsible for atherosclerosis. Peripheral artery disease (PAD) is a manifestation of systematic atherosclerosis. Whether the consequences of a low‐to‐moderate dose of radiation include increased risk of PAD remains to be determined. The purpose of this study was to examine the association between radiation exposure and prevalence of PAD among Japanese atomic bomb survivors.

Methods and Results

Radiation exposure from the atomic bombing was assessed in 3476 participants (41.1% men, mean age 74.8 years with SD 6.4 years) with a cross‐sectional survey in 2010 to 2014. Left‐ and right‐side ankle‐brachial indexes and upstroke time (UT) were obtained using oscillometric VP‐2000. PAD was defined as an ankle‐brachial index of 1.0 or less or a prior history related to revascularization. UT was considered a sensitive marker of early‐stage PAD. Association between radiation exposure and PAD or UT was assessed using multivariable regression analyses with adjustment for potential confounding factors. Of 3476 participants, 79 (2.3%) were identified as having prevalent PAD. Multivariate logistic regression analysis indicated that radiation dose was unrelated to PAD prevalence (odds ratio, 0.83; 95% confidence interval [0.57‐1.21]). UT appeared to increase with radiation dose, but the increase was not statistically significant (1.09 ms/Gy; 95% confidence interval [−0.17 to 2.36]).

Conclusions

We found no clear association of radiation dose with PAD, but it remains to be determined whether UT is associated with radiation dose.

Effect of Heterogeneity in Background Incidence on Inference about the Solid-Cancer Radiation Dose Response in Atomic Bomb Survivors

A recent analysis of solid cancer incidence in the Life Span Study of atomic bomb survivors (Hiroshima and Nagasaki, Japan) found evidence of a nonlinear, upwardly curving radiation dose response among males but not among females. Further analysis of this new and unexpected finding was necessary. We used two approaches to investigate this finding. In one approach, we excluded individual cancer sites or groups of sites from all solid cancers. In the other approach, we used joint analysis to allow for heterogeneity in background-rate parameters across groups of cancers with dissimilar trends in background rates. Exclusion of a few sites led to the disappearance of curvature among males in the remaining collection of solid cancers; some of these influential sites have unique features in their background age-specific incidence that are not captured by a background-rate model fit to all solid cancers combined. Exclusion of a few sites also led to an appearance of curvature among females. Misspecification of background rates can cause bias in inference about the shape of the dose response, so heterogeneity of background rates might explain at least part of the all solid cancer dose-response difference in curvature between males and females. We conclude that analysis based on all solid cancers as a single outcome is not the optimal method to assess radiation risk for solid cancer in the Life Span Study; joint analysis with suitable choices of cancer groups might be preferable by allowing for background-rate heterogeneity across sites while providing greater power to assess radiation risk than analyses of individual sites.

Association of Weight Fluctuation With Mortality in Japanese Adults

IMPORTANCE

Weight cycling is associated with the risk of mortality from heart disease, but many studies have not distinguished between simple nonlinear (monotone) weight changes and more complex changes that reflect fluctuations.

OBJECTIVE

To assess whether extreme body weight variation is associated with mortality after controlling for nonlinear weight changes.

DESIGN, SETTING, AND PARTICIPANTS

In this prospective clinical cohort study, 4796 Japanese atomic bomb survivors were examined in the clinic as part of a biennial health examination and research program. The study consisted of a 20-year longitudinal baseline period (July 1, 1958, to June 30, 1978) and subsequent mortality follow-up of 27 years (July 1, 1978, to June 30, 2005) Participants were initially between the ages of 20 and 49 years during the baseline period and, throughout the baseline period, had no diagnoses of cardiovascular disease (CVD) or cancer and attended at least 7 of 10 scheduled examinations. Data analysis was performed from October 16, 2015, to May 13, 2016.

EXPOSURES

Residual variability in body mass index (BMI) during the baseline period.

MAIN OUTCOMES AND MEASURES

Outcomes were mortality from ischemic heart disease, cerebrovascular disease, other CVDs combined, other causes (except cancer), and cancer. Root mean squared error was calculated to capture individual residual variation in BMI after adjustment for baseline BMI trends, and the association of magnitude of residual variation with mortality was calculated as relative risk.

RESULTS

In total, 4796 persons (mean [SD] age, 35.0 [7.3] years at first baseline examination; 3252 [67.8%] female; mean [SD] BMI, 21.2 [2.8] at first baseline visit [20.6 (2.4) among men and 21.5 (2.9) among women]) participated in the study. During follow-up, 1550 participants died: 82 (5.3% of all deaths) of ischemic heart disease, 181 (11.7%) of cerebrovascular disease, 186 (12.0%) of other CVDs, 615 (39.7%) of cancer, and 486 (31.3%) of other causes. Magnitude of residual variation in weight was associated with all-cause mortality (relative risk, 1.25 for 1 U of additional variation; 95% CI, 1.06-1.47) and ischemic heart disease mortality (relative risk, 2.49; 95% CI, 1.41-4.38).

CONCLUSIONS AND RELEVANCE

The findings suggest that an association exists between weight variation and heart disease mortality and that weight loss interventions, if deemed to be necessary, should be considered carefully.

Effects of Omitting Non-confounding Predictors From General Relative-Risk Models for Binary Outcomes

Background

The effects, in terms of bias and precision, of omitting non-confounding predictive covariates from generalized linear models have been well studied, and it is known that such omission results in attenuation bias but increased precision with logistic regression. However, many epidemiologic risk analyses utilize alternative models that are not based on a linear predictor, and the effect of omitting non-confounding predictive covariates from such models has not been characterized.

Methods

We employed simulation to study the effects on risk estimation of omitting non-confounding predictive covariates from an excess relative risk (ERR) model and a general additive-multiplicative relative-risk mixture model for binary outcome data in a case-control setting. We also compared the results to the effects with ordinary logistic regression.

Results

For these commonly employed alternative relative-risk models, the bias was similar to that with logistic regression when the risk was small. More generally, the bias and standard error of the risk-parameter estimates demonstrated patterns that are similar to those with logistic regression, but with greater magnitude depending on the true value of the risk. The magnitude of bias and standard error had little relation to study size or underlying disease prevalence.

Conclusions

Prior conclusions regarding omitted covariates in logistic regression models can be qualitatively applied to the ERR and the general additive-multiplicative relative-risk mixture model without substantial change. Quantitatively, however, these alternative models may have slightly greater omitted-covariate bias, depending on the magnitude of the true risk being estimated.

Population Density in Hiroshima and Nagasaki Before the Bombings in 1945: Its Measurement and Impact on Radiation Risk Estimates in the Life Span Study of Atomic Bomb Survivors

In the Life Span Study cohort of atomic bomb survivors, differences in urbanicity between high-dose and low-dose survivors could confound the association between radiation dose and adverse outcomes. We obtained data on the population distribution in Hiroshima and Nagasaki before the 1945 bombings and quantified the impact of adjustment for population density on radiation risk estimates for mortality (1950-2003) and incident solid cancer (1958-2009). Population density ranged from 4,671 to 14,378 people/km2 in the urban region of Hiroshima and 5,748 to 19,149 people/km2 in the urban region of Nagasaki. Radiation risk estimates for solid cancer mortality were attenuated by 5.1% after adjustment for population density, but those for all-cause mortality and incident solid cancer were unchanged. There was no overall association between population density and adverse outcomes, but there was evidence that the association between density and mortality differed according to age at exposure. Among survivors who were 10-14 years of age in 1945, there was a positive association between population density and risk of all-cause mortality (per 5,000-people/km2 increase, relative risk = 1.053, 95% confidence interval: 1.027, 1.079) and solid cancer mortality (per 5,000-people/km2 increase, relative risk = 1.069, 95% confidence interval: 1.025, 1.115). Our results suggest that radiation risk estimates from the Life Span Study are not sensitive to unmeasured confounding by urban-rural differences.

Stepwise approach to SNP-set analysis illustrated with the Metabochip and colorectal cancer in Japanese Americans of the Multiethnic Cohort

BACKGROUND

Common variants have explained less than the amount of heritability expected for complex diseases, which has led to interest in less-common variants and more powerful approaches to the analysis of whole-genome scans. Because of low frequency (low statistical power), less-common variants are best analyzed using SNP-set methods such as gene-set or pathway-based analyses. However, there is as yet no clear consensus regarding how to focus in on potential risk variants following set-based analyses. We used a stepwise, telescoping approach to analyze common- and rare-variant data from the Illumina Metabochip array to assess genomic association with colorectal cancer (CRC) in the Japanese sub-population of the Multiethnic Cohort (676 cases, 7180 controls). We started with pathway analysis of SNPs that are in genes and pathways having known mechanistic roles in colorectal cancer, then focused on genes within the pathways that evidenced association with CRC, and finally assessed individual SNPs within the genes that evidenced association. Pathway SNPs downloaded from the dbSNP database were cross-matched with Metabochip SNPs and analyzed using the logistic kernel machine regression approach (logistic SNP-set kernel-machine association test, or sequence kernel association test; SKAT) and related methods.

RESULTS

The TGF-β and WNT pathways were associated with all CRC, and the WNT pathway was associated with colon cancer. Individual genes demonstrating the strongest associations were TGFBR2 in the TGF-β pathway and SMAD7 (which is involved in both the TGF-β and WNT pathways). As partial validation of our approach, a known CRC risk variant in SMAD7 (in both the TGF-β and WNT pathways: rs11874392) was associated with CRC risk in our data. We also detected two novel candidate CRC risk variants (rs13075948 and rs17025857) in TGFBR2, a gene known to be associated with CRC risk.

CONCLUSIONS

A stepwise, telescoping approach identified some potentially novel risk variants associated with colorectal cancer, so it may be a useful method for following up on results of set-based SNP analyses. Further work is required to assess the statistical characteristics of the approach, and additional applications should aid in better clarifying its utility.

Effect of follow-up period on minimal-significant dose in the atomic-bomb survivor studies

It was recently suggested that earlier reports on solid-cancer mortality and incidence in the Life Span Study of atomic-bomb survivors contain still-useful information about low-dose risk that should not be ignored, because longer follow-up may lead to attenuated estimates of low-dose risk due to longer time since exposure. Here it is demonstrated, through the use of all follow-up data and risk models stratified on period of follow-up (as opposed to sub-setting the data by follow-up period), that the appearance of risk attenuation over time may be the result of less-precise risk estimation-in particular, imprecise estimation of effect-modification parameters-in the earlier periods. Longer follow-up, in addition to allowing more-precise estimation of risk due to larger numbers of radiation-related cases, provides more-precise adjustment for background mortality or incidence and more-accurate assessment of risk modification by age at exposure and attained age. It is concluded that the latest follow-up data are most appropriate for inferring low-dose risk. Furthermore, if researchers are interested in effects of time since exposure, the most-recent follow-up data should be considered rather than the results of earlier reports.

Heart Disease Mortality in the Life Span Study, 1950-2008

Based on the findings from the Radiation Effects Research Foundation's studies of the cohort of Japanese atomic bomb survivors, it has been reported that total-body irradiation at 0.5-1.0 Gy could be responsible for increased rates of mortality from broad-based categories of cardiovascular disease (CVD), i.e., stroke and heart disease. However, CVD consists of various subtypes that have potentially different radiation dose responses, as well as subtype-specific risks that have not been fully evaluated. Potential problems with changes in the coding rules for the International Classification of Diseases (ICD) and the underlying causes and trends in CVD mortality in Japan also need to be considered. The goal of this study was to clarify the radiation risk of subtype-specific heart disease over different time periods. Radiation dose response was examined for mortality from several heart disease subtypes in 86,600 members of the Life Span Study (LSS) cohort during 1950-2008. These subtypes included ischemic heart disease (IHD), valvular heart disease (VHD), hypertensive organ damage (HOD) and heart failure (HF). Individual radiation doses ranged between 0 and 4 Gy. In addition to analyses for the total period, we examined specific periods, 1950-1968, 1969-1980, 1981-1994 and 1995-2008, corresponding to major developments in medical technologies and ICD code revisions. We observed significant positive associations between radiation dose and mortality from heart disease overall in 1950-2008 [excess relative risk or ERR/Gy (95% CI) = 0.14 (0.06, 0.22)]. Subtype-specific ERRs also positively increased with dose: 0.45 (0.13, 0.85) for VHD, 0.36 (0.10, 0.68) for HOD and 0.21 (0.07, 0.37) for HF, respectively. No significant departure from linearity was shown for the dose-response model. Although there was no evidence for a threshold in a model function, the lowest dose ranges with a statistically significant dose response were 0-0.7 Gy for heart disease overall and VHD, 0-1.5 Gy for HOD and 0-0.4 Gy for HF. No significant association between radiation exposure and IHD was observed in any model, although a quadratic model fit the best. The risk of HOD and rheumatic VHD increased significantly in the earliest periods [ERR/Gy = 0.59 (0.07, 1.32) and 1.34 (0.24, 3.16), respectively]. The risk of nonrheumatic VHD increased with calendar time and was significant in the latest period [ERR/Gy = 0.75 (0.02, 1.92)]. The risk of IHD, especially for myocardial infarction, tended to be elevated in the most recent period after 2001, where cautious interpretation is needed due to the uncertain validity of death diagnosis. Radiation risks of heart disease mortality in the LSS appeared to vary substantially among subtypes, indicating possible differences in radiation-induced pathogenesis. Trends in CVD rates in Japan during the long observation period may also impact risk analyses.

Interaction between a single exposure and age in cohort-based hazard rate models impacted the statistical distribution of age at onset

OBJECTIVE

Statistical interaction between a single, instantaneous exposure and attained age (age during follow-up; attained age = age at exposure + time since exposure) is used in risk analyses to assess potential effect modification by unmeasured factors correlated with age. However, the impact of such interaction on the statistical distribution of age-at-onset of outcome (disease or death) is infrequently assessed. We therefore explored the impact of such interaction on the shape of the onset-age distribution.

STUDY DESIGN AND SETTING

We use for illustration age-at-onset of radiation-related early menopause in a cohort of female Japanese Atomic Bomb Survivors. The statistical distribution of age-at-onset was derived from a parametric hazard rate model fit to the data, assuming an underlying Gaussian onset-age distribution among nonexposed women.

RESULTS

Commonly used forms of exposure-by-age (attained age) interaction led to unnatural estimates of the age-specific rate function and unreasonable estimates of the onset-age distribution among exposed women, including positive risk of menopause before menarche.

CONCLUSION

We recommend that researchers examine the distribution of age-at-onset and exposure-age interaction when conducting risk analyses. To distinguish this from potential etiologic interaction between exposure and unmeasured factors represented by age as a surrogate, richer models or additional data may be required.

Steroid hormone measurements from different types of assays in relation to body mass index and breast cancer risk in postmenopausal women: Reanalysis of eighteen prospective studies

Epidemiological studies have examined breast cancer risk in relation to sex hormone concentrations measured by different methods: "extraction" immunoassays (with prior purification by organic solvent extraction, with or without column chromatography), "direct" immunoassays (no prior extraction or column chromatography), and more recently with mass spectrometry-based assays. We describe the associations of estradiol, estrone and testosterone with both body mass index and breast cancer risk in postmenopausal women according to assay method, using data from a collaborative pooled analysis of 18 prospective studies. In general, hormone concentrations were highest in studies that used direct assays and lowest in studies that used mass spectrometry-based assays. Estradiol and estrone were strongly positively associated with body mass index, regardless of the assay method; testosterone was positively associated with body mass index for direct assays, but less clearly for extraction assays, and there were few data for mass spectrometry assays. The correlations of estradiol with body mass index, estrone and testosterone were lower for direct assays than for extraction and mass spectrometry assays, suggesting that the estimates from the direct assays were less precise. For breast cancer risk, all three hormones were strongly positively associated with risk regardless of assay method (except for testosterone by mass spectrometry where there were few data), with no statistically significant differences in the trends, but differences may emerge as new data accumulate. Future epidemiological and clinical research studies should continue to use the most accurate assays that are feasible within the design characteristics of each study.

A report from the 2013 international symposium: the evaluation of the effects of low-dose radiation exposure in the life span study of atomic bomb survivors and other similar studies

The RERF International Low-Dose Symposium was held on 5-6 December 2013 at the RERF campus in Hiroshima, Japan, to discuss the issues facing the Life Span Study (LSS) and other low-dose studies. Topics included the current status of low-dose risk detection, strategies for low-dose epidemiological and statistical research, methods to improve communication between epidemiologists and biologists, and the current status of radiological studies and tools. Key points made by the participants included the necessity of pooling materials over multiple studies to gain greater insight where data from single studies are insufficient; generating models that reflect epidemiological, statistical, and biological principles simultaneously; understanding confounders and effect modifiers in the current data; and taking into consideration less studied factors such as the impact of dose rate. It is the hope of all participants that this symposium be used as a trigger for further studies, especially those using pooled data, in order to reach a greater understanding of the health effects of low-dose radiation.

Effects of IL-10 haplotype and atomic bomb radiation exposure on gastric cancer risk

Gastric cancer (GC) is one of the cancers that reveal increased risk of mortality and incidence in atomic bomb survivors. The incidence of gastric cancer in the Life Span Study cohort of the Radiation Effects Research Foundation (RERF) increased with radiation dose (gender-averaged excess relative risk per Gy = 0.28) and remains high more than 65 years after exposure. To assess a possible role of gene-environment interaction, we examined the dose response for gastric cancer incidence based on immunosuppression-related IL-10 genotype, in a cohort study with 200 cancer cases (93 intestinal, 96 diffuse and 11 other types) among 4,690 atomic bomb survivors participating in an immunological substudy. Using a single haplotype block composed of four haplotype-tagging SNPs (comprising the major haplotype allele IL-10-ATTA and the minor haplotype allele IL-10-GGCG, which are categorized by IL-10 polymorphisms at -819A>G and -592T>G, +1177T>C and +1589A>G), multiplicative and additive models for joint effects of radiation and this IL-10 haplotyping were examined. The IL-10 minor haplotype allele(s) was a risk factor for intestinal type gastric cancer but not for diffuse type gastric cancer. Radiation was not associated with intestinal type gastric cancer. In diffuse type gastric cancer, the haplotype-specific excess relative risk (ERR) for radiation was statistically significant only in the major homozygote category of IL-10 (ERR = 0.46/Gy, P = 0.037), whereas estimated ERR for radiation with the minor IL-10 homozygotes was close to 0 and nonsignificant. Thus, the minor IL-10 haplotype might act to reduce the radiation related risk of diffuse-type gastric cancer. The results suggest that this IL-10 haplotyping might be involved in development of radiation-associated gastric cancer of the diffuse type, and that IL-10 haplotypes may explain individual differences in the radiation-related risk of gastric cancer.

Ionizing radiation exposure and the development of soft-tissue sarcomas in atomic-bomb survivors

BACKGROUND

Very high levels of ionizing radiation exposure have been associated with the development of soft-tissue sarcoma. The effects of lower levels of ionizing radiation on sarcoma development are unknown. This study addressed the role of low to moderately high levels of ionizing radiation exposure in the development of soft-tissue sarcoma.

METHODS

Based on the Life Span Study cohort of Japanese atomic-bomb survivors, 80,180 individuals were prospectively assessed for the development of primary soft-tissue sarcoma. Colon dose in gray (Gy), the excess relative risk, and the excess absolute rate per Gy absorbed ionizing radiation dose were assessed. Subject demographic, age-specific, and survival parameters were evaluated.

RESULTS

One hundred and four soft-tissue sarcomas were identified (mean colon dose = 0.18 Gy), associated with a 39% five-year survival rate. Mean ages at the time of the bombings and sarcoma diagnosis were 26.8 and 63.6 years, respectively. A linear dose-response model with an excess relative risk of 1.01 per Gy (95% confidence interval [CI]: 0.13 to 2.46; p = 0.019) and an excess absolute risk per Gy of 4.3 per 100,000 persons per year (95% CI: 1.1 to 8.9; p = 0.001) were noted in the development of soft-tissue sarcoma.

CONCLUSIONS

This is one of the largest and longest studies (fifty-six years from the time of exposure to the time of follow-up) to assess ionizing radiation effects on the development of soft-tissue sarcoma. This is the first study to suggest that lower levels of ionizing radiation may be associated with the development of soft-tissue sarcoma, with exposure of 1 Gy doubling the risk of soft-tissue sarcoma development (linear dose-response). The five-year survival rate of patients with soft-tissue sarcoma in this population was much lower than that reported elsewhere.

Conventional case-cohort design and analysis for studies of interaction

BACKGROUND

The case-cohort study design has received significant methodological attention in the statistical and epidemiological literature but has not been used as widely as other cohort-based sampling designs, such as the nested case-control design. Despite its efficiency and practicality for a wide range of epidemiological study purposes, researchers may not yet be aware of the fact that the design can be analysed using standard software with only minor adjustments. Furthermore, although the large number of options for design and analysis of case-cohort studies may be daunting, they can be reduced to a few simple recommendations.

METHODS

We review conventional methods for the design and analysis of case-cohort studies and describe empirical comparisons based on a study of radiation, gene polymorphisms and cancer in the Japanese atomic bomb survivor cohort.

RESULTS

Stratified, as opposed to simple, random subcohort selection is recommended, especially for studies of gene-environment interaction, which are notorious for lacking statistical power. Methods based on the score-unbiased exact pseudo-likelihood (or its analogue with stratified case-cohort data) are recommended for use in conjunction with the asymptotic variance estimator.

CONCLUSIONS

We present an example of how to implement case-cohort analysis methods using SPSS, a popular statistical package that lacks some of the features necessary to directly adapt and implement published methods based on other software platforms. We also illustrate case-control analysis using Epicure, which provides greater risk-modelling flexibility than other software. Our conclusions and recommendations should help investigators to better understand and apply the case-cohort design in epidemiological research.

Protecting privacy of shared epidemiologic data without compromising analysis potential

OBJECTIVE

Ensuring privacy of research subjects when epidemiologic data are shared with outside collaborators involves masking (modifying) the data, but overmasking can compromise utility (analysis potential). Methods of statistical disclosure control for protecting privacy may be impractical for individual researchers involved in small-scale collaborations.

METHODS

We investigated a simple approach based on measures of disclosure risk and analytical utility that are straightforward for epidemiologic researchers to derive. The method is illustrated using data from the Japanese Atomic-bomb Survivor population.

RESULTS

Masking by modest rounding did not adequately enhance security but rounding to remove several digits of relative accuracy effectively reduced the risk of identification without substantially reducing utility. Grouping or adding random noise led to noticeable bias.

CONCLUSIONS

When sharing epidemiologic data, it is recommended that masking be performed using rounding. Specific treatment should be determined separately in individual situations after consideration of the disclosure risks and analysis needs.

Associations of ionizing radiation and breast cancer-related serum hormone and growth factor levels in cancer-free female A-bomb survivors

Levels of exposure to ionizing radiation are increasing for women worldwide due to the widespread use of CT and other radiologic diagnostic modalities. Exposure to ionizing radiation as well as increased levels of estradiol and other sex hormones are acknowledged breast cancer risk factors, but the effects of whole-body radiation on serum hormone levels in cancer-free women are unknown. This study examined whether ionizing radiation exposure is associated with levels of serum hormones and other markers that may mediate radiation-associated breast cancer risk. Serum samples were measured from cancer-free women who attended biennial health examinations with a wide range of past radiation exposure levels (N  =  412, ages 26-79). The women were selected as controls for separate case-control studies from a cohort of A-bomb survivors. Outcome measures included serum levels of total estradiol, bioavailable estradiol, testosterone, progesterone, prolactin, insulin-like growth factor-1 (IGF1), insulin-like growth factor-binding protein 3 (IGFBP-3), and ferritin. Relationships were assessed using repeated-measures regression models fitted with generalized estimating equations. Geometric mean serum levels of total estradiol and bioavailable estradiol increased with 1 Gy of radiation dose among samples collected from postmenopausal women (17%(1Gy), 95% CI: 1%-36% and 21%(1Gy), 95% CI: 4%-40%, respectively), while they decreased in samples collected from premenopausal women (-11%(1Gy), 95% CI: -20%-1% and -12%(1Gy), 95% CI: -20%- -2%, respectively). Interactions by menopausal status were significant (P  =  0.003 and P < 0.001, respectively). Testosterone levels increased with radiation dose in postmenopausal samples (30.0%(1Gy), 95% CI: 13%-49%) while they marginally decreased in premenopausal samples (-10%(1Gy), 95% CI: -19%-0%) and the interaction by menopausal status was significant (P < 0.001). Serum levels of IGF1 increased linearly with radiation dose (11%(1Gy), 95% CI: 2%-18%) and there was a significant interaction by menopausal status (P  =  0.014). Radiation-associated changes in serum levels of estradiol, bioavailable estradiol, testosterone and IGF1 were modified by menopausal status at the time of collection. No associations with radiation were observed in serum levels of progesterone, prolactin, IGFBP-3 or ferritin.

Exposure to ionizing radiation and development of bone sarcoma: new insights based on atomic-bomb survivors of Hiroshima and Nagasaki

BACKGROUND

Radiation-induced bone sarcoma has been associated with high doses of ionizing radiation from therapeutic or occupation-related exposures. However, the development of bone sarcoma following exposure to lower doses of ionizing radiation remains speculative.

METHODS

A cohort analysis based on the Life Span Study (n = 120,321) was performed to assess the development of bone sarcoma in atomic-bomb survivors of Hiroshima and Nagasaki followed from 1958 to 2001. The excess relative risk per gray of ionizing radiation absorbed by the bone marrow was estimated. Additional subject demographic, survival, and clinical factors were evaluated.

RESULTS

Nineteen cases of bone sarcoma (in eleven males and eight females) were identified among the 80,181 subjects who met the inclusion criteria, corresponding to an incidence of 0.9 per 100,000 person-years. The mean ages at the time of the bombing and at diagnosis were 32.4 and 61.6 years, respectively. The mean bone marrow dose was 0.43 Gy. Osteosarcoma was the most commonly identified bone sarcoma. The most common bone sarcoma site was the pelvis. The overall unadjusted five-year survival rate was 25%. A dose threshold was found at 0.85 Gy (95% confidence interval, 0.12 to 1.85 Gy), with a linear dose-response association above this threshold. The linear slope equaled an excess relative risk of 7.5 per Gy (95% confidence interval, 1.34 to 23.14 per Gy) in excess of 0.85 Gy.

CONCLUSIONS

On the basis of what we believe is one of the longest and largest prospective studies assessing the development of bone sarcoma in individuals exposed to ionizing radiation, it appears that the development of radiation-induced bone sarcoma may be associated with exposure to much lower doses of ionizing radiation than have previously been reported. Such new insights may potentially improve bone sarcoma prevention measures and broaden our understanding of the role of ionizing radiation from various sources on the development of malignant tumors. This study stresses the need to become increasingly aware of the various health risks that may be attributable to even low levels of ionizing radiation exposure.

LEVEL OF EVIDENCE

Prognostic Level I. See Instructions to Authors for a complete description of levels of evidence.

Attributable risk for radiation in the presence of other risk factors

Two motivations for studying radiation risk are (1) to quantify the magnitude of risk as an aid to setting radiation protection standards and (2) to understand causality as an aid to assigning compensation for radiation exposed individuals whose disease or death may have been related to radiation exposure. Although it has long been known that radiation risk is modified by factors such as sex, age, and time, it is now apparent that radiation risk may also be modified by other risk factors, such as smoking, inflammation, genotype, and certain pathogens. Even apart from considerations of etiological interaction, the relative contribution of radiation to total burden of disease or death may depend on the level of background (spontaneous) risk of disease or death owing to those other factors if the joint effects do not multiply. Therefore, ignoring those other factors in assessing probability of causation for radiation (attributable fraction in epidemiological data) involves making a strong assumption about the joint effects. The concepts are discussed in detail and illustrated using results from studies on the Japanese atomic-bomb survivors.

Longitudinal trends of total white blood cell and differential white blood cell counts of atomic bomb survivors

In studying the late health effects of atomic-bomb (A-bomb) survivors, earlier findings were that white blood cell (WBC) count increased with radiation dose in cross-sectional studies. However, a persistent effect of radiation on WBC count and other risk factors has yet to be confirmed. The objectives of the present study were 1) to examine the longitudinal relationship between A-bomb radiation dose and WBC and differential WBC counts among A-bomb survivors and 2) to investigate the potential confounding risk factors (such as age at exposure and smoking status) as well as modification of the radiation dose-response. A total of 7,562 A-bomb survivors in Hiroshima and Nagasaki were included in this study from 1964-2004. A linear mixed model was applied using the repeated WBC measurements. During the study period, a secular downward trend of WBC count was observed. Radiation exposure was a significant risk factor for elevated WBC and differential WBC counts over time. A significant increase of WBC counts among survivors with high radiation dose (> 2 Gy) was detected in men exposed below the age of 20 and in women regardless of age at exposure. Effects on WBC of low dose radiation remain unclear, however. Cigarette smoking produced the most pronounced effect on WBC counts and its impact was much larger than that of radiation exposure.

RET/PTC rearrangements preferentially occurred in papillary thyroid cancer among atomic bomb survivors exposed to high radiation dose

A major early event in papillary thyroid carcinogenesis is constitutive activation of the mitogen-activated protein kinase signaling pathway caused by alterations of a single gene, typically rearrangements of the RET and NTRK1 genes or point mutations in the BRAF and RAS genes. In childhood papillary thyroid cancer, regardless of history of radiation exposure, RET/PTC rearrangements are a major event. Conversely, in adult-onset papillary thyroid cancer among the general population, the most common molecular event is BRAF(V600E) point mutation, not RET/PTC rearrangements. To clarify which gene alteration, chromosome aberration, or point mutation preferentially occurs in radiation-associated adult-onset papillary thyroid cancer, we have performed molecular analyses on RET/PTC rearrangements and BRAF(V600E) mutation in 71 papillary thyroid cancer cases among atomic bomb survivors (including 21 cases not exposed to atomic bomb radiation), in relation to radiation dose as well as time elapsed since atomic bomb radiation exposure. RET/PTC rearrangements showed significantly increased frequency with increased radiation dose (P(trend) = 0.002). In contrast, BRAF(V600E) mutation was less frequent in cases exposed to higher radiation dose (P(trend) < 0.001). Papillary thyroid cancer subjects harboring RET/PTC rearrangements developed this cancer earlier than did cases with BRAF(V600E) mutation (P = 0.03). These findings were confirmed by multivariate logistic regression analysis. These results suggest that RET/PTC rearrangements play an important role in radiation-associated thyroid carcinogenesis.

Improved estimates of cancer site-specific risks for A-bomb survivors

Pawel, D. J., Preston, D. L., Pierce, D. A. and Cologne, J. B. Improved Estimates of Cancer Site-Specific Risks for A-Bomb Survivors. Radiat. Res. 169, 87-98 (2008). Simple methods are investigated for improving summary site-specific radiogenic risk estimates. Estimates in this report are derived from cancer incidence data from the Life Span Study (LSS) cohort of A-bomb survivors that are followed up by the Radiation Effects Research Foundation (RERF). Estimates from the LSS of excess relative risk (ERR) for solid cancer sites have typically been derived separately for each site. Even though the data for this are extensive, the statistical imprecision in site-specific (organ-specific) risk estimates is substantial, and it is clear that a large portion of the site-specific variation in estimates is due to this imprecision. Empirical Bayes (EB) estimates offer a reasonable approach for moderating this variation. The simple version of EB estimates that we applied to the LSS data are weighted averages of a pooled overall estimate of ERR and separately derived site-specific estimates, with weights determined by the data. Results indicate that the EB estimates are most useful for sites such as esophageal or bladder cancer, for which the separately derived ERR estimates are less precise than for other sites.

The presence of BRAF point mutation in adult papillary thyroid carcinomas from atomic bomb survivors correlates with radiation dose

In papillary thyroid carcinogenesis, the constitutively activated mitogen-activated protein (MAP) kinase signaling pathway caused by a genetic alteration such as RET/PTC rearrangement or mutation of RAS and BRAF genes, is thought to be a major early event. Among these, the recently identified BRAF(V600E) mutation has been found at high frequency in adult patients with papillary thyroid carcinoma (PTC). However, the association between this mutation and radiation exposure in adult PTC is still unknown. In this study, we examined the BRAF(V600E) mutation in 64 PTCs among adult atomic bomb survivors in Hiroshima, Japan, comprising 17 nonexposed (0 mGy) and 47 exposed patients who developed the carcinoma after the bombing, and assessed the association of BRAF(V600E) mutation with clinico-pathological and epidemiological variables. The median radiation dose in PTCs with the BRAF(V600E) mutation was significantly lower than that without the mutation (18.5 vs.156.9 mGy, Wilcoxon rank-sum test, P=0.022). A significant difference was found in the median latency period (years elapsed from atomic bombing to diagnosis) between exposed patients with and without BRAF(V600E) mutation (29 vs. 21 yr, Wilcoxon rank-sum test, P=0.014). These findings were further confirmed by logistic regression analysis with BRAF(V600E) mutation status as a dependent variable and taking into account possible interactions between the variables. We found that the log-transformed radiation dose and latency period were independently associated with the BRAF(V600E) mutation (P=0.039 and P=0.010, respectively). These results suggest that involvement of BRAF mutation in thyroid carcinogenesis in exposed people may differ from that in the nonexposed people.

Human Fetuses do not Register Chromosome Damage Inflicted by Radiation Exposure in Lymphoid Precursor Cells except for a Small but Significant Effect at Low Doses

Human fetuses are thought to be highly sensitive to radiation exposure because diagnostic low-dose X rays have been suggested to increase the risk of childhood leukemia. However, animal studies generally have not demonstrated a high radiosensitivity of fetuses, and the underlying causes for the discrepancy remain unidentified. We examined atomic bomb survivors exposed in utero for translocation frequencies in blood lymphocytes at 40 years of age. Contrary to our expectation of a greater radiosensitivity in fetuses than in adults, the frequency did not increase with dose except for a small increase (less than 1%) at doses below 0.1 Sv, which was statistically significant. We interpret the results as indicating that fetal lymphoid precursor cells comprise two subpopulations. One is small in number, sensitive to the induction of both translocations and cell killing, but rapidly diminishing above 50 mSv. The other is the major fraction but is insensitive to registering damage expressed as chromosome aberrations. Our results provide a biological basis for resolving the long-standing controversy that a substantial risk of childhood leukemia is implicated in human fetuses exposed to low-dose X rays whereas animal studies involving mainly high-dose exposures generally do not confirm it.

Estimating the Number of Hematopoietic or Lymphoid Stem Cells Giving Rise to Clonal Chromosome Aberrations in Blood T Lymphocytes

Quantifying the proliferative capacity of long-term hematopoietic stem cells in humans is important for bone marrow transplantation and gene therapy. Obtaining appropriate data is difficult, however, because the experimental tools are limited. We hypothesized that tracking clonal descendants originating from hematopoietic stem cells would be possible if we used clonal chromosome aberrations as unique tags of individual hematopoietic stem cells in vivo. Using FISH, we screened 500 blood T lymphocytes from each of 513 atomic bomb survivors and detected 96 clones composed of at least three cells with identical aberrations. The number of clones was inversely related to their population size, which we interpreted to mean that the progenitor cells were heterogeneous in the number of progeny that they could produce. The absolute number of progenitor cells contributing to the formation of the observed clones was estimated as about two in an unexposed individual. Further, scrutiny of ten clones revealed that lymphocyte clones could originate roughly equally from hematopoietic stem cells or from mature T lymphocytes, thereby suggesting that the estimated two progenitor cells are shared as one hematopoietic stem cell and one mature T cell. Our model predicts that one out of ten people bears a non- aberrant clone comprising >10% of the total lymphocytes, which indicates that clonal expansions are common and probably are not health-threatening.

Prediction of clonal chromosome aberration frequency in human blood lymphocytes

We recently conducted a large-scale screening for clonal aberrations among atomic bomb survivors and proposed a model for the gross clonal composition of blood lymphocytes. Here we show an application of the model indicating that the number, m,of clones detectable by cytogenetic methods in an individual is predictable by the equation m= (1.8 + 6.4FG) x FP x n/500, where FG represents the estimated translocation frequency in the 46 chromosome set, FP is the observed translocation frequency with FISH or other methods, and nis the number of cells examined. Application of the equation to the results of seven other reports gave close agreement between the observed and calculated numbers of clones. Since the model assumes that clonal expansion is ubiquitous, and any translocation can be the constituent of a clone detectable by cytogenetic means, the vast majority of observed clonal expansions of these somatic cells are likely the result of random-hit events that are not detrimental to human health. Furthermore, since our model can predict the majority of clonal aberrations among Chernobyl workers who were examined 5-6 years after irradiation, clonal expansion seems to occur primarily within a few years after exposure to radiation, most likely being coupled with the process of recovery from radiation-induced injury in the lymphoid and hematopoietic systems.

Selecting controls for assessing interaction in nested case-control studies

BACKGROUND

Two methods for selecting controls in nested case-control studies--matching on X and counter matching on X--are compared when interest is in interaction between a risk factor X measured in the full cohort and another risk factor Z measured only in the case-control sample. This is important because matching provides efficiency gains relative to random sampling when X is uncommon and the interaction is positive (greater than multiplicative), whereas counter matching is generally efficient compared to random sampling.

METHODS

Matching and counter matching were compared to each other and to random sampling of controls for dichotomous X and Z. Comparison was by simulation, using as an example a published study of radiation and other risk factors for breast cancer in the Japanese atomic-bomb survivors, and by asymptotic relative efficiency calculations for a wide range of parameters specifying the prevalence of X and Z as well as the levels of correlation and interaction between them. Focus was on analyses utilizing general models for the joint risk of X and Z.

RESULTS

Counter-matching performed better than matching or random sampling in terms of efficiency for inference about interaction in the case of a rare risk factor X and uncorrelated risk factor Z. Further, more general, efficiency calculations demonstrated that counter-matching is generally efficient relative to matched case-control designs for studying interaction.

CONCLUSIONS

Because counter-matched designs may be analyzed using standard statistical methods and allow investigation of confounding of the effect of X, whereas matched designs require a non-standard approach when fitting general risk models and do not allow investigating the adjusted risk of X, it is concluded that counter-matching on X can be a superior alternative to matching on X in nested case-control studies of interaction when X is known at the time of case-control sampling.

Prevalence of anti-hepatitis C virus antibody and chronic liver disease among atomic bomb survivors

To investigate whether exposure to atomic bomb radiation altered the prevalence of hepatitis C virus (HCV) infection or accelerated the progress toward chronic hepatitis after HCV infection, the seropositivity of antibody to hepatitis C virus (anti-HCV) was determined for 6,121 participants in the Adult Health Study of atomic bomb survivors in Hiroshima and Nagasaki. The seropositivity of anti-HCV antibody was 2.5 times higher among those with a history of blood transfusion and 1.2 times higher among those with a family history of liver disease, whereas acupuncture showed no association with anti-HCV. Although the prevalence of anti-HCV was lower for survivors with positive dose estimates than for those with 0 dose (relative prevalence 0.84, P = 0.022), there was no evidence of a smooth dose-response relationship. However, these data suggested that the radiation dose response for chronic liver disease among HCV antibody-positive survivors may be greater than that among HCV antibody-negative survivors (slope ratio 20). In conclusion, no dose-response relationship was found between anti-HCV positivity and radiation dose; a possible increase in the radiation dose response of chronic liver disease among anti-HCV-positive individuals was found. Thus radiation exposure may accelerate the progress of chronic liver disease associated with hepatitis C virus infection.

Methods of estimation in log odds ratio regression models

McCullagh's (1984, Journal of the Royal Statistical Society, Series B 46, 250-256) approximation to the conditional maximum likelihood estimator in log odds ratio regression models is shown to have negligible asymptotic bias unless the odds ratios are large and the sample sizes in individual 2 X 2 tables are very small. In application to two sets of case-control data, it yields results virtually indistinguishable from those of the conditional analysis. A generalization of the Mantel-Haenszel estimator proposed by Davis (1985, Biometrics 41, 487-495) does not approximate the conditional results nearly as well.