Risk indicators in childhood malignancies

Efficacy of Bacillus Calmette-Guérin in Cancer Prevention and Its Putative Mechanisms

Bacillus Calmette-Guérin (BCG) is an attenuated strain of Mycobacterium bovis. Although it was developed as a prophylactic vaccine against tuberculosis (TB), researchers have also evaluated it for preventing cancer development or progression. These studies were inspired by the available data regarding the protective effects of microbial infection against cancers and an inverse relationship between TB and cancer mortality. Initial studies demonstrated the efficacy of BCG in preventing leukemia, melanoma and a few other cancers. However, mixed results were observed in later studies. Importantly, these studies have led to the successful use of BCG in the tertiary prevention of non-muscle invasive bladder cancer, wherein BCG therapy has been found to be more effective than chemotherapy. Moreover, in a recently published 60-year follow-up study, childhood BCG vaccination has been found to significantly prevent lung cancer development. In the present manuscript, we reviewed the studies evaluating the efficacy of BCG in cancer prevention and discussed its putative mechanisms. Also, we sought to explain the mixed results of BCG efficacy in preventing different cancers.

Vaccination and the Risk of Childhood Cancer-A Systematic Review and Meta-Analysis

INTRODUCTION

Infections may play a role in the etiology of childhood cancer and immunizations may be protective because vaccinations stimulate the immune system. Observational studies reported inconsistent associations between vaccination and risk of childhood cancer. Since a synthesis of the evidence is lacking, we conducted a meta-analysis stratified by histological and site-specific cancer.

METHODS

We performed a systematic review (CRD42020148579) following PRISMA guidelines and searched for literature in MEDLINE, Embase, and the Science Citation Index databases. We identified in three literature databases 7,594 different articles of which 35 met the inclusion criteria allowing for 27 analyses of 11 cancer outcomes after exposure to nine different types of vaccinations. We calculated summary odds ratios (ORs) and 95% confidence intervals (CIs) using random effects models.

RESULTS

We observed four inverse associations between childhood leukemia and certain vaccines as well as the number of vaccinations: OR 0.49 (95% CI = 0.32 to 0.74) for leukemia death after bacillus Calmette-Guérin vaccination; OR 0.76 (95% CI = 0.65 to 0.90) for acute lymphoblastic leukemia after Haemophilus influenzae type b vaccination; OR 0.57 (95% CI = 0.36 to 0.88) for leukemia; and OR 0.62 (95% CI = 0.46 to 0.85) for acute lymphoblastic leukemia after three or more vaccinations of any type. All other conducted analyses did not show any associations.

DISCUSSION

The results are consistent with the hypothesis that vaccinations reduce the risk of childhood leukemia. However, the robustness and validity of these results is limited due to the small number, substantial heterogeneity, and methodological limitations of available studies.

Early vaccination protects against childhood leukemia: A systematic review and meta-analysis

Leukemia is the most commonly diagnosed childhood cancer, although its etiology is still largely unknown. Growing evidence supports a role for infection in the etiology of acute lymphocytic leukemia (ALL), and the involvement of the immune system suggests that vaccination may also play a role. However, the findings presented in the published literature are inconsistent. Therefore, we conducted a PRISMA systematic review and meta-analysis. 14 studies were identified and meta-analyzed. Vaccinations studied comprised Bacillus Calmette-Guérin (BCG) vaccine, Triple vaccine, Hepatitis B vaccine (HBV), Polio, Measles, Rubella, Mumps, trivalent MMR vaccine and Haemophilus influenza type B (HiB) vaccine. We observed a protective association between any vaccination in the first year of life and risk of childhood leukemia (summary odds ratio (OR) 0.58 [95% confidence interval (CI) 0.36-0.91]). When individual vaccines were analysed, some evidence of an association was seen only for BCG (summary OR 0.73 [95% CI 0.50-1.08]). In conclusion, early vaccination appears to be associated with a reduced risk of childhood leukemia. This finding may be underpinned by the association observed for BCG. Given the relatively imprecise nature of the results of this meta-analysis, our findings should be interpreted cautiously and replicated in future studies.

Safety of Tetanus, Diphtheria, and Pertussis Vaccination During Pregnancy: A Systematic Review

OBJECTIVE

To assess antenatal, birth, and infant outcomes for pregnant women, fetuses, and infants after antenatal vaccination with any antigen present in combination pertussis vaccines.

DATA SOURCES

PubMed, EMBASE, Literature in the Health Sciences in Latin America and the Caribbean, ClinicalTrials.gov, Cochrane Library, and World Health Organization (inception to May 5, 2016).

METHODS OF STUDY SELECTION

Studies reporting outcomes for pregnant women, their fetus, or infant after antenatal exposure to either monovalent or combined tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) or inactivated polio vaccines were considered for inclusion.

RESULTS

A total of 21 studies were included in this review. Point estimates ranged from 0.47 to 1.50 for preterm birth (less than 37 weeks of gestation), 0.65-1.00 for small for gestational age (birth weight less than the 10th percentile), 0.36-0.85 for stillbirth, 0.16-1.00 for neonatal death, 0.76-1.20 for low birth weight (less than 2,500 g), and 0.20-0.91 for congenital anomalies. All lower 95% confidence intervals (CIs) were less than 1.0. Of three retrospective studies assessing chorioamnionitis after vaccination, one showed a small but statistically significant increase. Point estimates for all anomalies after antenatal tetanus toxoid vaccination ranged from 1.20 to 1.60 and had 95% CIs that crossed 1.0. There was substantial clinical and methodologic heterogeneity from mainly retrospective observational studies with an overall high risk of bias. Objective rates of fever were low, 3% or below, and more common systemic events observed included headache, malaise, and myalgia.

CONCLUSION

Evidence suggests that antenatal combined Tdap administered during the second or third trimester of pregnancy is not associated with clinically significant harms for the fetus or neonate. Medically attended events in pregnant women are similar between vaccinated and unvaccinated groups.

Multiple meningiomas in a woman irradiated in utero

Meningiomas are a common central nervous system tumour and radiation is a known risk factor for their development. In utero radiation exposure correlates to developmental abnormalities and carcinogenesis in a dose- and gestational age-related manner. Radiation induced meningioma has been reported in detail in the literature in patients who had been irradiated earlier in life. At the time of publication, there was no data on radiation exposure whilst in utero and meningioma. We report on a 42-year-old woman with multiple intracranial meningiomas and no other risk factors except a history of in utero exposure to low dose X-ray radiation at 12weeks gestational age.

Carcinogenic risks of prenatal ionizing radiation

The risk of cancer in offspring who have been exposed to diagnostic X-ray procedures while in utero has been debated for 55 years. High doses at high dose rates to the embryo or fetus (e.g. >0.5 Gy) increase the risk of cancer. This has been demonstrated in human epidemiology studies as well as in mammalian animal studies. Most pregnant women exposed to diagnostic X-ray procedures or the diagnostic use of radionuclides receive doses to the embryo or fetus <0.1 Gy. The risk of cancer in offspring exposed in utero at a low dose such as <0.1 Gy is controversial and has not been determined.

Risk of lymphoma and leukaemia after bacille Calmette-Guérin and smallpox vaccination: a Danish case-cohort study

Vaccines may have non-specific effects as suggested mainly in mortality studies from low-income countries. The objective was to examine the effects of BCG and smallpox vaccinations on subsequent risk of lymphoma and leukaemia in a Danish population experiencing rapid out-phasing of these vaccines. In a background cohort (N=47,622) from the Copenhagen School Health Records Register, cases of leukaemia (N=20) and lymphoma (N=51) were identified through the Danish Cancer Registry. The vaccination status of the cases was compared with the vaccination status of a 5% random sample (N=2073) of the background cohort and analysed in a case-cohort design. BCG vaccination reduced the risk of lymphomas (HR=0.49 (95% CI: 0.26-0.93)), whereas smallpox vaccination did not (HR=1.32 (0.56-3.08)). With the small number of leukaemia cases, the analysis of leukaemia had limited power (BCG vaccination HR=0.81 (0.31-2.16); smallpox vaccination HR=1.32 (0.49-3.53)). The present study with very reliable vaccine history information indicates a beneficial effect of BCG vaccination on the risk of lymphomas.

Children's exposure to diagnostic medical radiation and cancer risk: epidemiologic and dosimetric considerations

While the etiology of most childhood cancers is largely unknown, epidemiologic studies have consistently found an association between exposure to medical radiation during pregnancy and risk of childhood cancer in offspring. The relation between early life diagnostic radiation exposure and occurrence of pediatric cancer risks is less clear. This review summarizes current and historical estimated doses for common diagnostic radiologic procedures as well as the epidemiologic literature on the role of maternal prenatal, children's postnatal and parental preconception diagnostic radiologic procedures on subsequent risk of childhood malignancies. Risk estimates are presented according to factors such as the year of birth of the child, trimester and medical indication for the procedure, and the number of films taken. The paper also discusses limitations of the methods employed in epidemiologic studies to assess pediatric cancer risks, the effects on clinical practice of the results reported from the epidemiologic studies, and clinical and public health policy implications of the findings. Gaps in understanding and additional research needs are identified. Important research priorities include nationwide surveys to estimate fetal and childhood radiation doses from common diagnostic procedures, and epidemiologic studies to quantify pediatric and lifetime cancer risks from prenatal and early childhood exposures to diagnostic radiography, CT, and fluoroscopically guided procedures.

Birth weight, maternal weight and childhood leukaemia

There is mounting evidence that childhood leukaemia is associated with high birth weight, but few studies have examined the relationship between leukaemia and other perinatal factors that influence birth weight, such as maternal weight or gestational weight gain. This case-cohort study included 916 acute lymphocytic leukaemia (ALL) and 154 acute myeloid leukaemia (AML) cases diagnosed prior to age 10 years between 1985 and 2001 and born in New York State excluding New York City between 1978 and 2001. Controls (n=9686) were selected from the birth cohorts for the same years. Moderate increased risk of both ALL and AML was associated with birth weight 3500 g or more. For ALL, however, there was evidence of effect modification with birth weight and maternal prepregnancy weight. High birth weight was associated with ALL only when the mother was not overweight while heavier maternal weight was associated with ALL only when the infant was not high birth weight. Increased pregnancy-related weight gain was associated with ALL. For AML, birth weight under 3000 g and higher prepregnancy weight were both associated with increased risk. These findings suggest childhood leukaemia may be related to factors influencing abnormal fetal growth patterns.

Vaccination history and risk of childhood leukaemia

BACKGROUND

Previous studies on vaccination and childhood leukaemia generated inconsistent results.

METHODS

In the Northern California Childhood Leukaemia Study, a case-control study with incident cases and matched birth certificate controls, detailed written vaccination records were collected. A total of 323 cases aged 0-14 years at diagnosis and 409 controls were included in this analysis. All vaccinations were censored on the reference date (date of diagnosis for cases and the corresponding date for matched controls). Conditional logistic regression analysis was conducted, adjusting for potential confounding factors. A primary variable of interest is the number of administrations (doses) of various types of vaccines.

RESULTS

Vaccinations against diphtheria, pertussis, tetanus, poliomyelitis, measles, mumps, and rubella were not associated with the risk of leukaemia. The odds ratio for each dose of Haemophilus influenzae type b (Hib) vaccine was 0.81 (95% CI 0.68-0.96). Compared with children who received two or fewer doses of Hib vaccine, those who received three or more doses had a significantly reduced risk of childhood leukaemia (odds ratio = 0.55, 95% confidence interval 0.32-0.94). The number of doses of hepatitis B vaccine received was not associated with leukaemia risk.

CONCLUSIONS

Hib vaccination is associated with a reduced risk of childhood leukaemia. Future studies with detailed exposure assessment and large sample sizes are needed to further address the role of vaccinations in the etiology of childhood leukaemia.

Impact of vaccinations and infectious diseases on the risk of melanoma--evaluation of an EORTC case-control study

A significant correlation between a reduced risk of melanoma and BCG and vaccinia vaccination in early childhood or infectious diseases later in life has already been reported from the FEBrile Infections and Melanoma (FEBIM) multicentre case-control study. This correlation is further evaluated in this study based on 603 incident cases of malignant melanoma and 627 population controls in six European countries and Israel by means of a joint analysis of the influence of vaccinations and infectious diseases. In addition, the previously unconsidered impact of influenza vaccinations is evaluated for the whole study population. The strong effects of the frequently given BCG and vaccinia vaccinations in early childhood, as well as of uncommon previous severe infectious diseases, were apparently not cumulative. With the Odds Ratio (OR) being set at 1 in the absence of vaccinations and infectious diseases, the OR dropped to 0.37 (95% Confidence Interval (CI): 0.10-1.42) when subjects had experienced one or more severe infectious diseases, associated with a fever of > 38.5 degrees C, and had not been vaccinated with BCG or vaccinia. The OR was 0.29 (CI: 0.15-0.57) in those who had had a severe infectious disease and were vaccinated with either BCG or vaccinia and 0.33 (CI: 0.17-0.65) for those with 1 or more severe infectious diseases and who had received both vaccinations. We conclude that both vaccinations as well as previous episodes of having a severe infectious disease induced the same protective mechanism with regards to the risk of melanoma. Because of a 'masking effect' by the vaccinia vaccination, the protective effect of the BCG vaccination and of certain infectious diseases against cancer has remained undetected. The vaccinations contributed more to the protection of the population than a previous episode of having an infectious disease. In view of the termination of vaccinations with vaccinia in all countries and of BCG in many of them, these findings call for a re-evaluation of vaccination strategies.

Prophylactic pinning of the contralateral hip in slipped capital femoral epiphysis : evaluation of long-term outcome for the contralateral hip with use of decision analysis

BACKGROUND

The risk of a contralateral slip in patients who are first seen with a unilateral slipped capital femoral epiphysis has been reported to be 2335 times higher than the risk of an initial slip. The overall prevalence of bilaterality varies widely throughout the literature, with some reports indicating rates as high as 80%. This finding has led many authors to recommend prophylactic pinning of the contralateral asymptomatic hip in patients presenting with a unilateral slipped capital femoral epiphysis.

METHODS

A decision analysis model with probabilities for the occurrence of contralateral slip and for the severity of slip at different intervals of follow-up was used in the present study. These probabilities were compared with those for various outcomes when the contralateral hip is prophylactically pinned. Scores representing long-term outcome, according to the Iowa hip-rating system, were used in the model as a measure of utility. The probabilities of contralateral slip and the rates of slip severity were taken from large retrospective series. All meaningful clinical scenarios with regard to long-term outcome for the hip were considered in the model. Variables of uncertainty were subjected to sensitivity analyses in order to explore the effect on outcome over the range of plausible values for variables of interest.

RESULTS

The results showed a benefit in the long-term outcome for patients who had prophylactic pinning of the contralateral hip. The threshold level at which a benefit is obtained with prophylactic pinning is expressed according to the rates of sequential slip, rates of slips overlooked at follow-up, and complications associated with prophylactic pinning of the contralateral hip.

CONCLUSIONS

The decision model shows that, when pooled data are used to predict probabilities of sequential slip, treatment of the contralateral hip with prophylactic pinning is beneficial to the long-term outcome for that hip. When considering prophylactic pinning of the contralateral hip, the clinician should use sound clinical judgment with respect to the age, sex, and endocrine status of the patient. Long-term follow-up studies are needed to establish the efficacy of prophylactic pinning, but the predictions in the present study, which are based on findings in the literature, support the safety of this procedure.

Intrauterine exposure to diagnostic X rays and risk of childhood leukemia subtypes

The relationship between childhood leukemia and prenatal exposure to low-dose ionizing radiation remains debatable. This population-based case-control study investigated the association between prenatal exposure to diagnostic X-ray examinations (for different types of examinations and at different stages of pregnancy) and the risk of childhood lymphatic and myeloid leukemia. All children born and diagnosed with leukemia between 1973-1989 in Sweden (578 lymphatic and 74 myeloid) were selected as cases, and each was matched (by sex and year of birth) to a healthy control child (excluding Down's syndrome). Exposure data were abstracted blindly from all available medical records. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by conditional logistic regression. It was found that prenatal X-ray examinations resulting in direct fetal exposure were not associated with a significant overall increased risk for childhood leukemia (OR = 1.11, 95% CI 0.83-1.47), for lymphatic leukemia (OR = 1.04, 95% CI 0.77-1.40), or for myeloid leukemia (OR = 1.49, 95% CI 0.48-4.72). There was little evidence of a dose response or variation in risk by trimester of exposure or age at diagnosis. Thus X-ray examinations performed during pregnancy in the 1970s and 1980s in Sweden did not affect the risk of childhood leukemia discernibly.

Prevention of childhood leukemia by BCG vaccination in newborns? A population-based case-control study in Lower Saxony, Germany

Data from a case-control study in Lower Saxony, Germany, were used to assess whether the risk for childhood cancer may be reduced by bacille Calmette-Guérin (BCG) vaccination in the neonatal period. There were 420 newly diagnosed childhood cancer cases from the German cancer registry and 613 controls eligible for this study. A mailed questionnaire was completed during a telephone interview with parents. Details on the perinatal history were abstracted from the birth charts by nurses blinded to the children's case-control status. Complete information was available for 259 cases and for 323 controls. A total of 85% of the controls had been BCG vaccinated in the newborn period. The adjusted odds ratios for BCG vaccination were 0.90 (95% confidence interval; 0.51-1.61) for leukemia and 0.61 (95% confidence interval; 0.25-1.50) for other cancers. Based on these data the probability of a 50% or more reduction of more reduction of the cancer risk by BCG vaccination in the newborn period is small. The statistical power of this study, however, was not high enough to rule out a smaller, still relevant reduction in cancer risk.

Maternal and perinatal risk factors for childhood brain tumors (Sweden)

Childhood brain tumors (CBT) include a diversity of rare neoplasms of largely unknown etiology. To assess possible maternal and perinatal risk factors for CBT according to subtype, we carried out a nested (within Swedish birth-cohorts, 1973-89) case-control study, utilizing data from the nationwide Birth Registry. We ascertained incident brain tumor cases through linkage of the nationwide Birth and Cancer Registries and randomly selected five living controls from the former, matching each case on gender and birthdate. There were 570 CBT cases, including 205 low grade astrocytomas, 58 high grade astrocytomas, 93 medulloblastomas, 54 ependymomas, and 160 'others.' Risks for all brain tumors combined were elevated in relation to: (i) three maternal exposures-oral contraceptives prior to conception (odds ratios [OR] = 1.6, 95 percent confidence interval [CI] = 1.0-2.8), use of narcotics (OR = 1.3, CI = 1.0-1.6), or penthrane (OR = 1.5, CI = 1.1-2.0) during delivery); (ii) characteristics of neonatal distress (a combined variable including low one-minute Apgar score, asphyxia [OR = 1.5, CI = 1.1-2.0]) or treatments for neonatal distress (use of supplemental oxygen, ventilated on mask, use of incubator, scalp vein infusion, feeding with a jejunal tube [OR = 1.6, CI = 0.9-2.6]); and (iii) neonatal infections (OR = 2.4, CI = 1.5-4.0). Higher subtype-specific risks, observed for a few risk factors, did not differ significantly from the risk estimates for all subtypes combined for the corresponding risk factors. Childhood brain tumors were not associated significantly with other maternal reproductive, lifestyle, or disease factors; perinatal pain, anesthetic medications, birth-related complications; or with birthweight, birth defects, or early neonatal diseases. These findings suggest several new leads, but only weak evidence of brain tumor subtype-specific differences.

Birth characteristics of childhood cancer cases, controls, and their siblings

Reproductive characteristics of childhood cancer cases, controls, and their siblings were examined using data from a case-control study in the Denver, Colorado metropolitan area. Childhood cancer patients (n = 356) diagnosed from 1976 to 1983 were identified, and 242 were interviewed. Controls were selected by random digit dialing, with 212 interviews being completed (60% of eligibles). Extremes of birth weight were more common only among brain cancer cases. Patients were more often born preterm, particularly those with brain tumors [odds ratio (OR) = 6.1; 95% confidence interval (CI), 1.6-23.4] and were more likely to have birth defects (OR = 2.1; 95% CI, 0.9-5.0). Twins were more common among case siblings (OR = 2.6; 95% CI, 0.8-8.2). Low birth weight and preterm delivery among siblings were related only to soft tissue sarcoma. Birth defects were more common among case siblings, particularly leukemia cases (OR = 3.2; 95% CI, 1.3-7.7). Previous reports of elevated birth weight among cases and increased risk of miscarriage in case mothers were not corroborated, but associations with preterm delivery, high birth order, and birth defects among cases and birth defects and twinning among cases siblings encourage additional evaluation.

Viruses, clusters and clustering of childhood leukaemia: a new perspective?

Clusters of childhood leukaemia have, during a lengthy and controversial history, focussed attention on two alternative putative aetiological agents: infections and localised environmental pollution. In the United Kingdom emphasis is currently placed on the latter because of reports of localised clusters in the vicinity of two nuclear reprocessing plants. Now the most recent studies of spatial clustering in the United Kingdom also support the hypothesis that a substantial population of cases of childhood acute lymphoblastic leukaemia (ALL) arise as a rare host response to certain patterns of exposure to common infectious agents--the aberrant response model. Relevant aspects of the epidemiology of ALL are reviewed from this perspective and the hypothesis shown to be capable of unifying reported associations with different types of risk factor. It is probable that specific agent(s) are involved though none have been identified and these may share many epidemiological characteristics of herpes viruses. The possible relevance of these results to associations with prenatal parental occupational exposures to dusts and ionising radiation is explored.

Incidence of childhood cancer in twins

The incidence of childhood cancer in twins was evaluated by linking a roster of 30,925 twins born in Connecticut (United States) between 1930 and 1969 with the Connecticut Tumor Registry. Cancer, exclusive of nonmelanoma skin cancer, was identified in 19 females and 12 males under 15 years of age. The incidence rate among twins was 7.9 cancers per 100,000 person-years (PY) overall, and 9.7 and 6.1 per 100,000 PYs for females and males, respectively. Four of 13 leukemias occurred in two female twin pairs, representing concordance rates of 18 percent overall and 29 percent for like-sex pairs, which are somewhat higher than values reported previously. The number of cancers expected was computed on the assumption that twins experienced the same sex-, age-, and calendar time-specific cancer rates as recorded for all Connecticut-born children. Because active follow-up of individuals was not conducted, an adjustment to person-years of observation was made to account for childhood mortality, including the high perinatal mortality characteristic of twins. Childhood cancer was 30 percent less frequent than expected (standardized incidence ratio [SIR] = 0.7; 95 percent confidence interval [CI] = 0.5-0.9), a deficit that is marginally greater than those found in previous studies. Both leukemia (SIR = 0.8; CI = 0.4-1.4), and all other cancers combined (SIR = 0.6; CI = 0.3-0.9) occurred less often than expected. The deficit was greater among males (SIR = 0.5; CI = 0.2-0.8) than among females (SIR = 0.9; CI = 0.5-1.4) and was especially pronounced among males younger than five years (SIR = 0.2; CI = 0.0-0.7). The data support the view that twins, particularly male twins, have a lower risk of childhood cancer than single-born children. Any added risk for twins associated with their greater frequency of exposure to prenatal X-rays appears to have been insufficient to offset an 'effect' of twinning per se. Possible explanations for this finding include (i) the low birthweight distribution of twins, or (ii) selective early mortality of twin fetuses or neonates who would otherwise have developed a clinical cancer.

Childhood brain tumor risk in relation to birth characteristics

A population-based case-control study was conducted utilizing linked cancer registry and birth certificate data to examine potential associations between selected birth characteristics and the occurrence of brain tumors in children. Cases (n = 157) were those children ages 10 and under who were born in Washington state and who were diagnosed with a primary brain tumor between 1974 and 1986. Controls were randomly selected from the Washington State birth files and were matched 5:1 to cases on year and county of birth. A limited number of positive findings emerged from the study. Results suggested that high birthweight may be related to an increased risk of childhood brain tumor (odds ratio (OR) = 1.4, 95% CI 1.0-2.0 for all histologies combined; OR = 1.9, 95% CI 1.1-3.1 for astrocytomas). The risk of astrocytoma was also observed to be associated with older maternal age (OR = 2.2, 95% CI 1.2-4.0) and a history of prior fetal death(s) (OR = 1.9, 95% CI 1.0-3.8).

Birth weight as a risk factor for childhood acute lymphoblastic leukemia

Increased birth weight previously has been reported to be associated with childhood acute leukemia although the etiologic importance of this finding remains unclear. To further assess birth weight and associated parameters as a risk factor for childhood leukemia, a case/control study was performed using children with acute lymphoblastic leukemia (ALL) born in the state of Minnesota and diagnosed since 1969. Data obtained from birth registrations of 219 cases were compared with two control groups matched on date and county of birth (group I) or year of birth (group II). No significant differences were observed in mean birth weights of cases and controls. Statistically significant associations with birth weights greater than 3800 g were identified in cases diagnosed within the first 4 years of life. No associations were found between birth weight and ALL for case children diagnosed after 4 years of age. Factors that might be associated with increased birth weight, including maternal age, birth order, length of gestation, and socioeconomic status as measured by paternal education, were not found to be associated with an increased risk for ALL. The significance of the finding of high birth weight as a risk factor for childhood ALL remains unknown but suggests that pregnancy-related events may be of importance in the etiology of ALL in young children.

Prenatal x-ray exposure and childhood cancer in twins

We conducted a case-control study to investigate the relation between prenatal exposure to x-rays and childhood cancer, including leukemia, in over 32,000 twins born in Connecticut from 1930 to 1969. Twins as opposed to single births were chosen for study to reduce the likelihood of medical selection bias, since twins were often exposed to x-rays to diagnose the twin pregnancy or to determine fetal positioning before delivery and not because of medical conditions that may conceivably pre-dispose to cancer. Each of 31 incident cases of cancer, identified by linking the Connecticut twin and tumor registries, was matched with four twin controls according to sex, year of birth, and race. Records of hospitals, radiologists, and private physicians were searched for histories of x-ray exposure and other potentially important risk factors. Documented prenatal x-ray exposures were found for 39 per cent of the cases (12 of 31) and for 26 per cent of the controls (28 of 109). No other pregnancy, delivery, or maternal conditions were associated with cancer risk except low birth weight: 38 per cent of the cases as compared with 25 per cent of the controls weighed under 2.27 kg at birth. When birth weight was adjusted for, twins in whom leukemia or other childhood cancer developed were twice as likely to have been exposed to x-rays in utero as twins who were free of disease (relative risk, 2.4; 95 per cent confidence interval, 1.0 to 5.9). The results, though based on small numbers, provide further evidence that low-dose prenatal irradiation may increase the risk of childhood cancer.

Childhood cancer and parental occupation in Finland

A case-control study was conducted of the occupations of parents of children under 15 with diagnosed malignancies. The total series contained all childhood cancers cases reported to the Finnish Cancer Registry during the period 1959-75. The parental occupations, recorded at the time of pregnancy, were collected from maternity welfare centres. The cases were analysed as a singly group or as subgroups according to the diagnoses-brain tumours, leukaemia, and all other malignancies. The maternal occupations found more frequently among cases than controls included farmers' wives (1959-68 only), pharmacists, saleswomen, bakers, and factory work of an vehicle driving, machine repair, painting, and the work of men who gave an academic degree as their occupation. Some of these occupations involve possible exposure to harmful chemicals, although chance correlations cannot be excluded.

Transplacental carcinogens and mutagens: childhood cancer, malformations, and abortions as risk indicators

Childhood cancer, malformations, and spontaneous abortions in Finland were analyzed according to the parents' occupations. Children of women working in the food industry and farming and of men working in motor vehicle driving and farming appeared to have an elevated risk of cancer. Women in industrial and construction occupations had an increased risk of having malformed children and spontaneous abortions.

BCG vaccination and the incidence of lymphomas and leukaemia

BCG vaccination has been claimed to prevent leukaemia, but there is also concern that it might increase the risk of Hodgkin's disease and other lymphomas. Both hypotheses were tested by comparing mortality and registration rates in cohorts of children from the North and South Islands of New Zealand. When school-children were offered vaccination in both islands, subsequent death rates from lymphomas and leukaemia were similar in the two islands. After withdrawal of vaccination in the South Island, mortality and registration rates for Hodgkin's disease remained similar in the two islands, but there was significant excess of deaths from non-Hodgkin lymphomas in the North Island. The difference in the registration rates for these tumours was much smaller than the difference in mortality rates and was not statistically significant. There was no evidence that BCG vaccination in the North Island prevented leukemia. These findings and the results of other studies suggest that proposals for BCG vaccination against leukaemia are unwise.

Cancer in the offspring of fathers in hydrocarbon-related occupations

A case-control study has been conducted to see whether a hydrocarbon-related occupation of the father at the time of conception constitutes a risk factor for malignant disease in the offspring. The series comprised 852 cancer cases from the Finnish Cancer Registry and 852 controls matched for date of birth and domicile. The father's occupation for both the cases and controls was ascertained from the records of antenatal clinics. No significant associations were found between the commonest types of childhood cancer and hydrocarbon-related occupations--that is, motor-vehicle mechanics, machinists, miners, painters, and motor-vehicle drivers. Risk ratio 2 was excluded from most of the 95% confidence intervals for children under 15 years of age. The results do not support the hypothesis that there is an excess risk of cancer in the children of fathers in hydrocarbon-related occupations.