Early-onset breast cancer in A-bomb survivors

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

Subtle excess in lifetime cancer risk related to CT scanning in Spanish young people

BACKGROUND

CT scan is a life-saving medical diagnostic tool, entailing higher levels of ionising radiation exposure than conventional radiography, which may result in an increase in cancer risk, particularly in children. Information about the use and potential health effects of CT scan imaging among young people in Spain is scarce.

OBJECTIVE

This paper aims to estimate the number of radiation-related cancer cases which can be expected due to the use of CT scanning in Spanish children and young adults in a single year (2013).

METHODS

The 2013 distribution of number and types of CT scans performed in young people was obtained for Catalonia and extrapolated to the whole Spain. Organ doses were estimated based on the technical characteristics of 17,406 CT examinations extracted from radiology records. Age and sex-specific data on cancer incidence and life tables were obtained for the Spanish population. Age and sex-specific risk models developed by the Committee on Health Risks of Exposure to Low Levels of Ionizing Radiations (BEIR VII) and Berrington de Gonzalez were used, together, with the dose estimates to derive the lifetime attributable risks of cancer in Spain due to one year of CT scanning and project the number of future cancer cases to be expected.

RESULTS

In 2013, 105,802 CT scans were estimated to have been performed in people younger than age 21. It was estimated that a total of 168.6 cancer cases (95% CrI: 30.1-421.1) will arise over life due to the ionising radiation exposure received during these CTs. Lifetime attributable risks per 100,000 exposed patients were highest for breast and lung cancer. The largest proportion of CTs was to the head and neck and hence the highest numbers of projected cancer cases were of thyroid and oral cavity/pharynx.

CONCLUSIONS

Despite the undeniable medical effectiveness of CT scans, this risk assessment suggests a small excess in cancer cases which underlines the need for justification and optimisation in paediatric scanning. Given the intrinsic uncertainties of these risk projection exercises, care should be taken when interpreting the predicted risks.

Ionizing Radiation and Human Health: Reviewing Models of Exposure and Mechanisms of Cellular Damage. An Epigenetic Perspective

We reviewed available evidence in medical literature concerning experimental models of exposure to ionizing radiations (IR) and their mechanisms of producing damages on living organisms. The traditional model is based on the theory of “stochastic breakage” of one or both strands of the DNA double helix. According to this model, high doses may cause the breaks, potentially lethal to the cell by damaging both DNA strands, while low doses of IR would cause essentially single strands breaks, easily repairable, resulting in no permanent damages. The available evidence makes this classical model increasingly less acceptable, because the exposure to low doses of IR seems to have carcinogenic effects, even after years or decades, both in the exposed individuals and in subsequent generations. In addition, the cells that survived the exposure to low doses, despite being apparently normal, accumulate damages that become evident in their progeny, such as nonclonal chromosomal aberrations, which can be found even in cells not directly irradiated due to the exchange of molecular signals and complex tissue reactions involving neighboring or distant cells. For all these reasons, a paradigm shift is needed, based on evidence and epigenetics.

The Role of Computed Tomography Scanning of the Thorax in the Initial Assessment of Gestational Trophoblastic Neoplasia

Objective

The aim of this study was to determine whether lesions found on computed tomography (CT) imaging of the thorax would affect FIGO (International Federation of Gynecology and Obstetrics) 2000 risk score and/or alter clinical management.

Methods

The Sheffield Trophoblastic Disease database was searched for all new patients registered for staging/scoring investigations between January 1, 2006, and June 30, 2010. The FIGO 2000 score was noted and then recalculated using information from CT scan reports. Where a change of risk score would have affected a patient’s management, the case notes were further reviewed.

Results

191 patients had undergone both modalities of imaging. Using standard FIGO scoring, 169 and 22 patients were noted to be at low and high risk, respectively. Using information from CT imaging, only a further 20 patients would have been reclassified as high risk. Fifteen of these “new” high-risk patients required salvage treatment with intravenous chemotherapy; all were cured.

Conclusions

With no potential advantage in terms of patient outcome and significantly increased radiation dose, there is little justification for routine CT imaging of the thorax in the initial assessment of new patients with gestational trophoblastic neoplasia.

Usefulness of a lead shielding device for reducing the radiation dose to tissues outside the primary beams during CT

PURPOSE

This study was done to investigate the efficacy of a lead shield in protecting the tissues outside the primary beams, such as the breast and thyroid, by measurement of the entrance skin dose during CT of the brain, neck, abdomen, and lumbar spine.

MATERIALS AND METHODS

Institutional Review Board approval was obtained. This study included 150 patients (male:female 25:125, age range 15-45 years). In females, brain, lumbar spine, and abdominal CT scans, pre-/post-contrast neck CT scans, and post-contrast liver dynamic CT scans were performed. In males, brain CT scans only were performed. Breast shielding was performed in all females, and thyroid shielding was conducted in patients with brain CT. During all CT studies, the left breast or left thyroid was shielded using a lead shield, and the contralateral side was left unshielded. Thus, each breast or thyroid measurement had its own control for the same demographic data. The efficacy of the shielding of both breasts and thyroids during CT was assessed.

RESULTS

During brain, abdominal, lumbar, pre-/post-contrast neck, and post-contrast liver dynamic CT, 33.5, 26.0, 17.4, 26.5, and 16.2 % of the breast skin dose were reduced, respectively. During brain CT, the thyroid skin dose was reduced by 17.9 % (females) and 20.6 % (males). There were statistically significant differences in the skin doses of shielded organs (p < 0.05). Breast shielding during neck and liver dynamic CT was the most effective compared with breast or thyroid shielding during other CT scans.

CONCLUSIONS

We recommend breast shielding during neck and liver dynamic CT in young female patients to avoid unnecessary radiation exposure.

Comparison of radiation dose estimates and scan performance in pediatric high-resolution thoracic CT for volumetric 320-detector row, helical 64-detector row, and noncontiguous axial scan acquisitions

RATIONALE AND OBJECTIVES

Efforts to decrease radiation exposure during pediatric high-resolution thoracic computed tomography (HRCT), while maintaining diagnostic image quality, are imperative. The objective of this investigation was to compare organ doses and scan performance for pediatric HRCT using volume, helical, and noncontiguous axial acquisitions.

MATERIALS AND METHODS

Thoracic organ doses were measured using 20 metal oxide semiconductor field-effect transistor dosimeters. Mean and median organ doses and scan durations were determined and compared for three acquisition modes in a 5-year-old anthropomorphic phantom using similar clinical pediatric scan parameters. Image noise was measured and compared in identical regions within the thorax.

RESULTS

There was a significantly lower dose in lung (1.8 vs 2.7 mGy, P < .02) and thymus (2.3 vs 2.7 mGy, P < .02) between volume and noncontiguous axial modes and in lung (1.8 vs 2.3 mGy, P < .02), breast (1.8 vs 2.6 mGy, P < .02), and thymus (2.3 vs 2.4 mGy, P < .02) between volume and helical modes. There was a significantly lower median image noise for volume compared to helical and axial modes in lung (55.6 vs 79.3 and 70.7) and soft tissue (76.0 vs 111.3 and 89.9). Scan times for volume, helical, and noncontiguous axial acquisitions were 0.35, 3.9, and 24.5 seconds, respectively.

CONCLUSION

Volumetric HRCT provides an opportunity for thoracic organ dose and image noise reduction, at significantly faster scanning speeds, which may benefit pediatric patients undergoing surveillance studies for diffuse lung disease.

Pulmonary embolism

Pulmonary embolism (PE) remains one of the most challenging medical diseases in the emergency department. PE is a potentially life threatening diagnosis that is seen in patients with chest pain and/or dyspnea but can span the clinical spectrum of medical presentations. In addition, it does not have any particular clinical feature, laboratory test, or diagnostic modality that can independently and confidently exclude its possibility. This article offers a review of PE in the emergency department. It emphasizes the appropriate determination of pretest probability, the approach to diagnosis and management, and special considerations related to pregnancy and radiation exposure.

Peripartum pulmonary embolism

Pregnancy is an example of Virchow's triad predisposing to the development of venous thromboembolism (VTE). Specific risk factors for antepartum and postpartum VTE have been identified. The diagnosis of pulmonary embolism in pregnancy is complicated by the physiologic changes of pregnancy as well as physicians' apprehension about ordering radiologic studies during pregnancy because of concerns with fetal well-being. Therapy for VTE is complicated by pregnancy physiology affecting medication pharmacokinetics and bioavailability, and the unpredictable occurrence of labor during therapeutic anticoagulation.

Radiation dosimetry and safety issues in the investigation of pulmonary embolism

When considering the investigation of the patient with possible pulmonary embolism, one needs to balance the likelihood of disease and the diagnostic utility of the test against the risks associated with the investigation. Both computed tomography pulmonary angiography (CTPA) and the ventilation/perfusion (V/Q) scan involve exposure to ionizing radiation. The effect of low-level ionizing radiation remains an issue of some controversy. CTPA delivers a greater effective dose and, in particular, greater doses to breast tissue, than the V/Q scan (typically 10-70 mGy for CTPA vs <1.5 mGy for V/Q to breast). Since breast tissue is particularly radiosensitive in younger women, the V/Q study has an advantage over CTPA in this group. In the pregnant patient, fetal exposure has been raised as a concern. In fact, there is typically only low fetal exposure from either study (<1 mGy). The CTPA does deliver less fetal exposure, particularly in the first trimester, but the difference between CTPA and V/Q scan is small when compared with the difference in dose to maternal breast from the 2 investigations. The "as low as reasonably achievable" (ie, ALARA) principle favors the use of V/Q scans in young women, assuming the diagnostic power of the 2 tests is comparable. CTPA requires a contrast injection that can cause adverse reactions in a small number of patients. No significant risk, however, has been demonstrated with the radiopharmaceuticals involved in V/Q scans.

Timing of menarche and first birth in relation to risk of breast cancer in A-bomb survivors

BACKGROUND

The length of the interval between age at menarche and age at first birth is positively associated with breast cancer risk. We examined the risk of breast cancer in atomic bomb survivors to investigate whether women exposed to radiation between menarche and first birth had a higher risk of radiogenic breast cancer than women exposed at the same age but outside this interval.

METHODS

Women (n = 30,113) were classified into three reproductive status at the time of the bombings (ATB) categories (premenarche, between menarche and first birth, or after first birth). Poisson regression was used to test the primary hypothesis.

RESULTS

When the background rate of breast cancer was taken to depend on city, age ATB, and attained age only, the radiation-related excess relative risk (ERR) varied significantly among the three categories (P = 0.049). However, after controlling for significant heterogeneity in the baseline risk of breast cancer between reproductive status ATB groups (P < 0.001), no significant heterogeneity (P = 0.88) was observed in the ERR, with an ERR per Gy of 1.36 [95% confidence interval (CI), 0.54-2.75] for women exposed between menarche and first birth ATB, and 1.07 (95% CI, 0.22-3.62) and 1.53 (95% CI, 0.63-2.90) for those exposed premenarche or after first birth, respectively.

CONCLUSIONS

The radiation-associated risk of breast cancer does not vary significantly by reproductive status ATB.

IMPACT

It is possible that radiation exerts similar carcinogenic effects on the breast regardless of its stage of differentiation, or that the differences in radiosensitivity are too small to be detected in this cohort.

Low-dose radiation epidemiology studies: status and issues

Although the Japanese atomic bomb study and radiotherapy studies have clearly documented cancer risks from high-dose radiation exposures, radiation risk assessment groups have long recognized that protracted or low exposures to low-linear energy transfer radiations are key radiation protection concerns because these are far more common than high-exposure scenarios. Epidemiologic studies of human populations with low-dose or low dose-rate exposures are one approach to addressing those concerns. A number of large studies of radiation workers (Chernobyl clean-up workers, U.S. and Chinese radiological technologists, and the 15-country worker study) or of persons exposed to environmental radiation at moderate to low levels (residents near Techa River, Semipalatinsk, Chernobyl, or nuclear facilities) have been conducted. A variety of studies of medical radiation exposures (multiple-fluoroscopy, diagnostic (131)I, scatter radiation doses from radiotherapy, etc.) also are of interest. Key results from these studies are summarized and compared with risk estimates from the Japanese atomic bomb study. Ideally, one would like the low-dose and low dose-rate studies to guide radiation risk estimation regarding the shape of the dose-response curve, DDREF (dose and dose-rate effectiveness factor), and risk at low doses. However, the degree to which low-dose studies can do so is subject to various limitations, especially those pertaining to dosimetric uncertainties and limited statistical power. The identification of individuals who are particularly susceptible to radiation cancer induction also is of high interest in terms of occupational and medical radiation protection. Several examples of studies of radiation-related cancer susceptibility are discussed, but none thus far have clearly identified radiation-susceptible genotypes.

Radiation-induced mammary carcinogenesis in rodent models: what's different from chemical carcinogenesis?

Ionizing radiation is one of a few well-characterized etiologic factors of human breast cancer. Laboratory rodents serve as useful experimental models for investigating dose responses and mechanisms of cancer development. Using these models, a lot of information has been accumulated about mammary gland cancer, which can be induced by both chemical carcinogens and radiation. In this review, we first list some experimental rodent models of breast cancer induction. We then focus on several topics that are important in understanding the mechanisms and risk modification of breast cancer development, and compare radiation and chemical carcinogenesis models. We will focus on the pathology and natural history of cancer development in these models, genetic changes observed in induced cancers, indirect effects of carcinogens, and finally risk modification by reproductive factors and age at exposure to the carcinogens. In addition, we summarize the knowledge available on mammary stem/progenitor cells as a potential target of carcinogens. Comparison of chemical and radiation carcinogenesis models on these topics indicates certain similarities, but it also indicates clear differences in several important aspects, such as genetic alterations of induced cancers and modification of susceptibility by age and reproductive factors. Identification of the target cell type and relevant translational research for human risk management may be among the important issues that are addressed by radiation carcinogenesis models.JRRS Incentive Award in 2009.

Multiple diagnostic X-rays for spine deformities and risk of breast cancer

BACKGROUND

Ionizing radiation is a well-established human mammary carcinogen. Women historically monitored by radiography at young ages for abnormal spinal curvature are an exposed population suitable for investigating radiation-related risk and its variation by modifying factors. In this historic cohort, 95% of daily dose increments (when exposure to the breast occurred) were under 2.4 cGy, with mean 1.1 cGy.

METHODS

A retrospective cohort of 3,010 women, diagnosed with spinal curvature between 1912 and 1965 in 14 U.S. pediatric orthopedic centers and who completed a questionnaire by telephone interview or mail survey in 1992, were studied for risk of breast cancer by radiation dose to the breast (mean, 12 cGy) after adjustment for established breast cancer risk factors.

RESULTS

A borderline-significant radiation dose response (excess relative risk/Gy = 2.86; P = 0.058; one-tailed P = 0.029) was observed during 118,905 woman-years of follow-up (median, 35.5 years) based on 78 cases of invasive breast cancer. The dose response was significantly greater (P = 0.03) for women who reported a family history of breast cancer in first- or second-degree relatives (excess relative risk/Gy = 8.37; 95% confidence interval, 1.50-28.16). Radiation-related risk did not vary significantly by stage of reproductive development at exposure.

CONCLUSIONS

Assuming that repair of radiation-related DNA damage requires at most a few hours, our data argue against existence of a low-dose threshold on the order of 1 to 3 cGy for radiation exposure contributing to breast carcinogenesis. The possibility that a family history of breast cancer may have enhanced a carcinogenic radiation effect requires confirmation in other studies.

Newer modalities for detection of pulmonary emboli

Pulmonary embolism (PE) is the third most common cardiovascular disease after myocardial infarction and stroke in the United States. Early and accurate diagnosis of this condition is imperative because many patients die within hours of presentation. Clinical and laboratory tests can be used to accurately determine the pretest probability of PE. When necessary, imaging techniques are then used to exclude or diagnose PE. Pulmonary angiography is the reference standard for the diagnosis of PE, but it is invasive and has a high morbidity and mortality rate. Ventilation and perfusion (V/Q) scanning in the past has been recommended as the initial diagnostic test for PE; however, this technique also has limitations. Recently, new modalities for the diagnosis and exclusion of PE have been evaluated. These techniques include V/Q single photon emission computed tomography (SPECT), single- and multi-detected computed tomography, and magnetic resonance angiography (MRA) including gadolinium-enhanced MRA, real-time magnetic resonance imaging (RT-MR), and magnetic resonance perfusion imaging.

Radiation Dose to the Female Breast from 16-MDCT Body Protocols

OBJECTIVE

The objective of our study was to determine the radiation dose to the female breast from current 16-MDCT body examinations.

MATERIALS AND METHODS

Metal oxide semiconductor field effect transistor (MOSFET) detectors were placed in four quadrants of the breast of a female-configured anthropomorphic phantom to determine radiation dose to the breast. Imaging was performed on a 16-MDCT scanner (LightSpeed, GE Healthcare) using current clinical protocols designed to assess pulmonary embolus (PE) (140 kVp, 380 mA, 0.8-sec rotation, 16 x 1.25 mm collimation), appendicitis (140 kVp, 340 mA, 0.5-sec rotation, 16 x 0.625 mm collimation), and renal calculus (140 kVp, 160 mA, 0.5-sec rotation, 16 x 0.625 mm collimation).

RESULTS

Radiation dose to the breast ranged from 4 to 6 cGy for the PE protocol and up to 1-2 cGy in the inferior aspect of the right breast and lateral aspect of the left breast for the appendicitis protocol. The renal calculus protocol yielded less than 150 microGy absorbed breast dose.

CONCLUSION

Current clinical chest and abdomen protocols result in vairable radiation doses to the breast. The magnitude of exposure may have implications for imaging strategies.

Radiation and breast cancer: a review of current evidence

This paper summarizes current knowledge on ionizing radiation-associated breast cancer in the context of established breast cancer risk factors, the radiation dose-response relationship, and modifiers of dose response, taking into account epidemiological studies and animal experiments. Available epidemiological data support a linear dose-response relationship down to doses as low as about 100 mSv. However, the magnitude of risk per unit dose depends strongly on when radiation exposure occurs: exposure before the age of 20 years carries the greatest risk. Other characteristics that may influence the magnitude of dose-specific risk include attained age (that is, age at observation for risk), age at first full-term birth, parity, and possibly a history of benign breast disease, exposure to radiation while pregnant, and genetic factors.

The cancer epidemiology of radiation

Ionizing radiation has been the subject of intense epidemiological investigation. Studies have demonstrated that exposure to moderate-to-high levels can cause most forms of cancer, leukaemia and cancers of the breast, lung and thyroid being particularly sensitive to induction by radiation, especially at young ages at exposure. Predominant among these studies is the Life Span Study of the cohort of survivors of the atomic bombings of Japan in 1945, but substantial evidence is derived from groups exposed for medical reasons, occupationally or environmentally. Notable among these other groups are underground hard rock miners who inhaled radioactive radon gas and its decay products, large numbers of patients irradiated therapeutically and workers who received high doses in the nuclear weapons programme of the former USSR. The degree of carcinogenic risk arising from low levels of exposure is more contentious, but the available evidence points to an increased risk that is approximately proportional to the dose received. Epidemiological investigations of nonionizing radiation have established ultraviolet radiation as a cause of skin cancer. However, the evidence for a carcinogenic effect of other forms of nonionizing radiation, such as those associated with mobile telephones or electricity transmission lines, is not convincing, although the possibility of a link between childhood leukaemia and extremely low-frequency electromagnetic fields cannot be dismissed entirely.

Incidence of female breast cancer among atomic bomb survivors, Hiroshima and Nagasaki, 1950-1990

An incidence survey of the Life Span Study (LSS) population found 1093 breast cancers among 1059 breast cancer cases diagnosed during 1950-1990. As in earlier breast cancer surveys of this population, a linear and statistically highly significant radiation dose response was found. In the analysis, particular attention was paid to modification of radiation dose response by age at exposure (e) and attained age (a). Dose-specific excess relative risk (ERR(1Sv)) decreased with increasing values of e and a. A linear dose-response model analysis, with e and a as exponential age modifiers, did not conclusively discriminate between the two variables as modifiers of dose response. A modified isotonic regression approach, requiring only that ERR(1Sv) be monotonic in age, provides a fresh perspective indicating that both e and a are important modifiers of dose response. Exposure before age 20 was associated with higher ERR(1Sv) compared to exposure at older ages, with no evidence of consistent variation by exposure age for ages under 20. ERR(1Sv) was observed to decline with increasing attained age, with by far the largest drop around age 35. Possible explanations for these observations are discussed, along with research approaches that might provide more information.

Breast cancer risk among the survivors of atomic bomb and patients exposed to therapeutic ionising radiation

Radiation induced breast cancer is a highly complex phenomenon, which most likely involves the accumulation of several genetic and epigenetic events. Studies of atomic bomb survivors, patients who underwent multiple fluoroscopic examinations during treatment for pulmonary tuberculosis, those who received therapeutic radiation for benign breast disease, such as acute post-partum mastitis, or those with an enlarged thymus or skin haemangioma and patients with Hodgkin's disease treated by mantle radiotherapy established that the risk of breast cancer increases with exposure to ionising radiation. The carcinogenic effect of therapeutic or accidental radiation is highest when exposure occurs during childhood and exposure after age 40 imparts low or minimal risk. The risk of bilateral breast cancer is not significantly increased in the survivors of atomic bomb and therapeutic radiations. Fractionated exposures for therapeutic radiation are similar to a single exposure of the same total dose in their ability to induce breast cancer; this risk remains high for many years after exposure. Younger age at first full term pregnancy confers a protective effect against the risk of breast cancer in the survivors of atomic bomb but long-term data on this beneficial effect after therapeutic radiation is not available.

Screening women at high risk of breast cancer on the basis of evidence

Geneticists are able to identify the risk of breast cancer. Strategies on offer include prevention, early diagnosis by screening, and prophylactic surgery. This paper analyses the evidence for offering screening. The radiation dose of mammography has been measured, but the risk is not fully known. Mammography screening of women of 40-50 years in the normal population has known effect. Little evidence is available for women under 40 years or for women with genetic susceptibility to breast cancer. Dense parenchymal pattern is associated with high grade cancers, and is both a risk factor and a reason for impaired screening sensitivity. Whether this applies to younger women or women at high risk is speculative. The pathological features of the cancers in gene carriers show differences from those occurring in normal women. This work should be correlated with imaging features. There is no literature to support the use of newer imaging methods in these women. Ultrasound and MRI avoid radiation and may be useful in dense breasts. SestaMIBI and PET scanning are not yet mature enough for screening, and may never have such a role. Any newer modality must be subjected to a formal randomised trial before being offered to screen women at high risk.

Heterozygous germline ATM mutations do not contribute to radiation-associated malignancies after Hodgkin's disease

PURPOSE

The successful treatment of Hodgkin's disease has been associated with an increased incidence of secondary malignancies. To investigate whether genetic factors contribute to the development of secondary tumors, we collected family cancer histories and performed mutational analysis of the ataxia-telangiectasia (AT) gene, ATM, in a cohort of Hodgkin's disease survivors with secondary malignancies. ATM was chosen for evaluation because of the increased radiosensitivity of cells derived from AT patients and obligate heterozygotes and the epidemiologic observation that AT carriers are at increased risk for radiation-induced breast cancer.

PATIENTS AND METHODS

Fifty-two patients who developed one or more neoplasms after treatment for Hodgkin's disease participated in this study. Personal and family histories of cancer were obtained through patient interviews and review of medical records. ATM mutational analysis was performed using a yeast-based protein truncation assay.

RESULTS

Seventy-six secondary neoplasms were observed in this cohort of 52 Hodgkin's disease survivors, with 18 patients (35%) developing more than one secondary neoplasm. Positive family histories of cancer were present in 11 (21%) of 52 patients, compared with three (4%) of 68 Hodgkin's disease patients in a comparison cohort who did not develop secondary neoplasms (P =.008; Fisher's exact test). No germline ATM mutations were identified, resulting in an estimated AT carrier frequency in this population of 0% (90% confidence interval, 0% to 4%).

CONCLUSION

Analysis of the number of tumors per individual and the family history of cancer in our cohort suggests that genetic factors may contribute to development of secondary neoplasms in a subset of Hodgkin's disease survivors. Mutational analysis, however, does not support a significant role for heterozygous truncating ATM mutations. Future studies evaluating other genes involved in DNA damage response pathways are warranted.

The linear no-threshold debate: where do we go from here?

For the past several years, the LNT (linear no-threshold) theory has come under attack within the scientific community. Analysis of a number of epidemiological studies of the Japanese survivors of the atomic bombings and workers exposed to low level radiation suggest that the LNT philosophy is overly conservative, and low-level radiation may be less dangerous than commonly believed. Proponents of current standards argue that risk conservatism is justified because low level risks remain uncertain and it is prudent public health policy; LNT opponents maintain that regulatory compliance costs are excessive, and there is now substantial scientific information arguing against the LNT model. Regulators use the LNT theory in the standards setting process to predict numbers of cancers due to exposure to low level radiation because direct observations of radiation-induced cancers in populations exposed to low level radiation are difficult. The LNT model is simplistic and provides a conservative estimate of risk. Abandoning the LNT philosophy and relaxing regulations would have enormous economic implications. However, alternative models to predict risk at low dose are as difficult to justify as the LNT model. Perhaps exposure limits should be based on model-independent approaches. There is no requirement that exposure limits be based on any predictive model. It is prudent to base exposure limits on what is known directly about health effects of radiation exposure of human populations.

Efficacy and toxicity of radiation in preparative regimens for pediatric stem cell transplantation. II: Deleterious consequences

There has been a dramatic improvement in the treatment of both allogeneic and autologous stem cell transplants, especially in children and young adults. However, attempts to apply more intensive conditioning treatments to the more refractory pediatric malignancies have also increased the risks of deleterious consequences. This review examines the risks, and reports important variations in the toxic effects of using different conditioning techniques.

Human cancer predisposition and the implications for radiological protection

It is well established from clinical, epidemiological and laboratory studies that specific human germ line mutation can predispose to spontaneously arising cancer. Some of the responsible genes have been characterized at the molecular level and evidence is rapidly accumulating on mechanistic aspects of the problem. A major outstanding issue is the extent to which genetically determined cancer predisposition in man interacts with exposures to environmental genotoxic agents such as ionizing radiation. This brief review considers the current position regarding the different forms and frequencies of cancer-predisposing mutations in the human population and provides an interim view of the possible implications for protection of man from ionizing radiation.

A case-control interview study of breast cancer among Japanese A-bomb survivors. II. Interactions with radiation dose

Three breast cancer risk factors were evaluated in terms of their interactions with radiation dose in a case-control interview study of Japanese A-bomb survivors. Cases and controls were matched on age at the time of the bombings and radiation dose, and dose-related risk was estimated from cohort rather than case-control data. Each factor--age at first full-term pregnancy, number of deliveries, and cumulative lactation period summed over births--conformed reasonably well to a multiplicative interaction model with radiation dose (the additive interactive model, in which the absolute excess risk associated with a factor is assumed to be independent of radiation dose, was rejected). An important implication of the finding is that early age at first full-term pregnancy, multiple births, and lengthy cumulative lactation are all protective against radiation-related, as well as baseline, breast cancer. Analyses by age at exposure to radiation suggest that, among women exposed to radiation in childhood or adolescence, a first full-term pregnancy at an early age following exposure may be protective against radiation-related risk.