Environmental radon exposure and breast cancer risk in the Nurses' Health Study II

BACKGROUND

Radon and its decay products, a source of ionizing radiation, are primarily inhaled and can deliver a radiation dose to breast tissue, where they may continue to decay and emit DNA damage-inducing particles. Few studies have examined the relationship between radon and breast cancer.

METHODS

The Nurses' Health Study II (NHSII) includes U.S. female registered nurses who completed biennial questionnaires since 1989. Self-reported breast cancer was confirmed from medical records. County-level radon exposures were linked with geocoded residential addresses updated throughout follow-up. Time-varying Cox regression models adjusted for established breast cancer risk factors were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

From 1989 to 2013, 3966 invasive breast cancer cases occurred among 112,639 participants. Increasing radon exposure was not associated with breast cancer risk overall (adjusted HR comparing highest to lowest quintile = 1.06, 95% CI: 0.94, 1.21, p for trend = 0.30). However, women in the highest quintile of exposure (≥74.9 Bq/m3) had a suggested elevated risk of ER-/PR- breast cancer compared to women in the lowest quintile (<27.0 Bq/m3) (adjusted HR = 1.38, 95% CI: 0.97, 1.96, p for trend = 0.05). No association was observed for ER+/PR+ breast cancer.

CONCLUSIONS

Although we did not find an association between radon exposure and risk of overall or ER+/PR+ breast cancer, we observed a suggestive association with risk of ER-/PR- breast cancer.

Radium dial watches, a potentially hazardous legacy?

This study re-examines the risk to health from radium ((226)Ra) dial watches. Ambient dose equivalent rates have been measured for fifteen pocket watches giving results of up to 30 μSv h(-1) at a distance of 2 cm taken with a series 1000 mini-rad from the front face (arithmetic mean ambient dose equivalent for pocket watches being 13.2 μSv h(-1)). A pocket compass gave rise to a similar ambient dose equivalent rate, of 20 μSv h(-1), to the pocket watches, with its cover open. Eighteen wristwatches have also been assessed, but their dose rates are generally much lower (the arithmetic mean being 3.0 μSv h(-1)), although the highest ambient dose equivalent rate noted was 20 μSv h(-1). A phantom experiment using a TLD suggested an effective dose equivalent of 2.2 mSv/y from a 1 μCi (37 kBq) radium dial worn for 16 h/day throughout the year (dose rate 0.375 μSv h(-1)). For this condition we estimated maximum skin dose for our pocket watches as 16 mSv per year, with effective doses of 5.1 mSv and 1.169 mSv when worn in vest and trouser pockets respectively. This assumes exposure from the back of the watch which is generally around 60-67% of that from the front. The maximum skin dose from a wristwatch was 14 mSv, with 4.2 mSv effective dose in vest pocket. Radium ((226)Ra) decays to the radioactive gas radon ((222)Rn), and atmospheric radon concentration measurements taken around a pocket watch in a small sealed glass sphere recorded 18,728 B qm(-3). All watches were placed in a room with a RAD7 real-time radon detector. Radon concentration average was 259±9 Bq m(-3) over 16 h, compared to background average over 24h of 1.02 Bq m(-3). Over 6 weeks highs of the order of 2000 Bq m(-3) were routinely recorded when the heating/ventilation system in the room was operating at reduced rates, peaking at over 3000 Bq m(-3) on several occasions. Estimates of the activity of (226)Ra in the watches ranged from 0.063 to 1.063 μCi (2.31 to 39.31 kBq) for pocket watches and from 0.013 to 0.875 μCi (0.46 to 32.38 kBq) for wrist watches. The risk from old watches containing radium appears to have been largely forgotten today. This paper indicates a health risk, particular to collectors, but with knowledge and appropriate precautions the potential risks can be reduced.

The effect of neutering on the risk of mammary tumours in dogs--a systematic review

A commonly-stated advantage of neutering bitches is a significant reduction in the risk of mammary tumours, however the evidence for this has not previously been assessed by systematic review. The objectives of this study were to estimate the magnitude and strength of evidence for any effect of neutering, or age of neutering, on the risk of mammary tumours in bitches. A systematic review was conducted based on Cochrane guidelines. Peer-reviewed analytic journal articles in English were eligible and were assessed for risk of bias by two reviewers independently. Of 11,149 search results, 13 reports in English-language peer-reviewed journals addressed the association between neutering/age at neutering and mammary tumours. Nine were judged to have a high risk of bias. The remaining four were classified as having a moderate risk of bias. One study found an association between neutering and a reduced risk of mammary tumours. Two studies found no evidence of an association. One reported "some protective effect" of neutering on the risk of mammary tumours, but no numbers were presented. Due to the limited evidence available and the risk of bias in the published results, the evidence that neutering reduces the risk of mammary neoplasia, and the evidence that age at neutering has an effect, are judged to be weak and are not a sound basis for firm recommendations.

Ancestry of beagles in lifespan studies of radionuclide toxicity at the University of Utah

Analysis of the ancestry of the 1,262 lifespan beagles (LSB) entered into lifespan studies at the Radiobiology Division, University of Utah, beginning in 1952 and ending in 1980, indicated that about 97% of ancestor citations in the various pedigrees were of only 10 breeding animals (breeders) among breeders within the beagle colony. In turn, just 18 AKC-registered "champion" beagles from outside of this colony (founders) accounted for about 98% of all ancestor citations among founders for the LSB. We conclude from this study that the animals used in the lifespan radionuclide experiments can be considered to be somewhat genetically interrelated.

Does low dose internal radiation increase lifespan?

No significant differences in lifespan could be established between control dogs and dogs given 241Am, 228Th, 90Sr, 228Ra, 226Ra or monomeric 239Pu at low dosage levels that induced less than 10% skeletal malignancies (low dose animals) in the Utah beagle colony when all dogs surviving at least 1 y were included in the analysis and dogs given individual radionuclides were considered separately or together. Censoring or exclusion of dogs from these groups that were diagnosed with skeletal malignancies or that died in a gran mal epileptic seizure made no important difference to these results. Therefore, an enhanced lifespan of low dose dogs as compared with controls could not be established. It is concluded that low doses from internal (mainly skeletal) deposits of these radionuclides probably do not benefit the survival of individuals so exposed.

Survival and bone tumor hazard from internal deposition of 226Ra in beagles

The survival of 132 young adult control beagles and 117 beagles receiving graded injections of 226Ra ranging from 0.27 kBq kg-1 to 384.2 kBq kg-1 body mass was analyzed. The hazards of natural deaths, all deaths in injection groups, and deaths by bone tumors were assumed to follow a Weibull distribution with a common shape factor of 6.3. Only the scale factors of the Weibull distributions depend on the injection level. There were no significant sex differences. The relative risk with respect to controls for all causes of death increases up to 6,925 for 384.2 kBq kg-1. The dependence of the scale factors for all deaths and death by bone tumors on injected activity was fitted to an empirical regression model, which also contains a term representing radiation-caused deaths other than bone tumors. The risk of bone tumors increases nearly as the square of the injected activity, whereas the risk of the other radiation caused deaths increases approximately in proportion to the injected activity. By means of the regression model, it is possible to predict median survival times for all deaths, bone tumor and non-bone tumor deaths for an arbitrary intake level. Also, simple expressions for the fraction of animals with bone tumors and other radiation-caused deaths can be derived. The empirical model of bone tumor induction, which was based on results from a single injection design, can be generalized to an arbitrary systemic intake schema. This is achieved by using the average dose and dose rate to the skeleton as indices of detriment. Applying the generalized model, it was confirmed that no significant differences in survival can be expected for two groups of beagles receiving multiple injections, if compared to the corresponding single injection groups of about the same total activity. The general model also predicts that even extensive protraction of the intake would increase the survival times only to a very limited extent.

Review of 239Pu and 226Ra effects in beagles

A long term biological study has been completed that was designed to assess the predicted effects in humans of internally deposited 239Pu by comparison with 226Ra in beagles. Herein we summarize for the first time results of several previous reports about the effects of these two radionuclides in our beagles in an attempt to elucidate what has been learned since the beginning of the study in the early 1950's. Perhaps the most important finding was that bone surface-seeking plutonium is more toxic at equal mean skeletal radiation doses (<3 Gy for 239Pu, <20 Gy for 226Ra) than bone volume-seeking radium for the induction of skeletal malignancy by about a factor of 16 for a single intravenous injection of monomeric 239Pu. In addition, ancillary studies have shown that when plutonium transfers continuously onto bone surfaces from a depot of particulate 239Pu in phagocytic cells, its relative toxicity per Gy average skeletal dose is enhanced by about a factor of 2. Juvenile animals or dogs injected as mature adults were only about half as sensitive for equal mean skeletal doses as dogs injected as young adults. Male and female dogs were about equally sensitive to radiation of the skeleton by either radionuclide. Findings about radiation-induced fractures are summarized as well as data on the induction of soft-tissue malignancies by 239Pu or 226Ra. Natural survival was not affected at the lower dosage levels of either 226Ra or 239Pu as compared with control dogs given no radioactivity, but the survival of animals at higher levels was reduced. No additional life-shortening effects beyond those attributable to occurrence of radiation-induced malignancies or other radiation-induced effects were suggested by analysis of data for low dosage levels.

Does longevity in beagles injected with bone-seeking radionuclides depend upon radiation dose in the absence of known radiation effects?

Regression analyses of longevity as a function of skeletal radiation dose among groups of beagles injected with 226Ra, 228Ra, 228Th, 241Am, 90Sr or monomeric 239Pu suggested that at low doses and dose-rates (those at which induced effects are low), age at death seems to be independent of dose when animals dying with specific radiation effects were excluded, although longevity does appear to be a function of dose when animals dying with established radiation effects and at all doses were included. We conclude tentatively that, for mammals receiving skeletal dose from bone-seeking radionuclides at low doses and low dose-rates, longevity may not be dependent upon skeletal radiation dose in the absence of radiation-induced malignancies or other radiation effects.

Classification and behavior of canine mammary epithelial neoplasms based on life-span observations in beagles

As part of a study of the effects of low-level radiation, 1,343 Beagles, including 671 males and 672 females, were evaluated over their full lifetime for the occurrence of mammary neoplasia; there were 139 control males and 138 control females and 532 irradiated males and 534 irradiated females. All nodules found in surgical specimens or at necropsy were evaluated histologically. The overall incidence, metastasis and recurrence rates, and contribution to mortality of mammary neoplasms were determined. Based on this unique opportunity to correlate morphologic characteristics with ultimate biological behavior of all mammary tumors in a defined canine population, we propose a histogenetically based reclassification of epithelial mammary tumors. Of the 672 female dogs, 70.8% (476) had at least one mammary neoplasm; 60.7% (408) had more than one. Two male dogs had mammary neoplasms. Of 1,639 mammary carcinomas in the 672 females, 18.7% (307) were classified as ductular carcinomas (arising from the small interlobular or intralobular ductules), whereas 80.7% (1,322) were classified as adenocarcinomas of other histogenetic origin. Of 73 fatal carcinomas, ductular carcinomas accounted for 48 fatalities (65.8%), whereas other adenocarcinomas accounted for only 20 fatalities (27.4%). Radiation had no effect on this ratio. Ductular carcinomas also had a higher rate of metastasis than did adenocarcinomas. Existing classifications of mammary carcinomas do not recognize the characteristic morphologic features, the degree of malignancy, and the prognostic importance of these ductular carcinomas. Metastasis rates did not differ between simple and complex carcinomas or between those lesions and adenocarcinomas in mixed tumors. True carcinosarcomas metastasized more frequently (100%, or 5/5) than did adenocarcinomas in mixed tumors (34.4%, or 22/64), emphasizing the importance of not lumping these tumors under the classification of malignant mixed tumors.

Dosimetry and pathology of 237Np in female rats

Female Sprague-Dawley rats, 10-12-week old and weighing about 240 g, were injected intravenously with 237Np-nitrate. In the toxicological study 77 rats served as controls and 28 rats per group received single doses of 5.2 and 26 kBq, respectively, per kg body weight. In addition, 12 rats of each injection level, sacrificed at defined points in time, were used for dosimetric studies. During the whole life-span the body weight and 237Np whole body-content of each animal were recorded. After death a detailed pathological examination was made of each animal in the cronical study. One day after injection 48% of the injected activity was in the skeleton, 9.3% in the liver, 3% in the kidneys and 4.4% in the rest of the organs. Whereas in all organs the activity decreased very fast, the half-life in the skeleton was about 1400 days. The bodyweights were comparable in the three groups, but the life span decreased from 800 days (control group) to 644 days after injection (26 kBq kg-1 body weight group). The main lesions in the female rats were mammary tumors (73%) and pituitary gland tumors (52%). With increasing activity the incidence of pituary gland tumors decreased and that of osteosarcomas increased from 1.3% (control group) to 32% (26 kBq kg-1 body weight group), whereas the remaining lesions showed no influence on the activity.