Endocrine disruptors: Challenges and future directions in epidemiologic research

Public concern about the impact of endocrine disrupting chemicals (EDCs) on both humans and the environment is growing steadily. Epidemiologic research provides key information towards our understanding of the relationship between environmental exposures like EDCs and human health outcomes. Intended for researchers in disciplines complementary to epidemiology, this paper highlights the importance and challenges of epidemiologic research in order to present the key elements pertaining to the design and interpretation of an epidemiologic study on EDCs. The conduct of observational studies on EDCs derives from a thoughtful research question, which will help determine the subsequent methodological choices surrounding the careful selection of the study population (including the comparison group), the adequate ascertainment of exposure(s) and outcome(s) of interest, and the application of methodological and statistical concepts more specific to epidemiology. The interpretation of epidemiologic results may be arduous due to the latency occurring between EDC exposure and certain outcome(s), the complexity in capturing EDC exposure(s), and traditional methodological and statistical issues that also deserve consideration (e.g., confounding, effect modification, non-monotonic responses). Moving forward, we strongly advocate for an integrative approach of expertise in the fields of epidemiology, exposure science, risk assessment and toxicology to adequately study the health risks associated with EDCs while tackling their challenges.

Inter-rater reliability of occupational exposure assessment in a case-control study of female breast cancer

The objective of this paper was to estimate the inter-rater reliability of expert assessments of occupational exposures. An inter-rater reliability sub-study was conducted within a population-based case-control study of postmenopausal breast cancer. Detailed information on lifetime occupational histories was obtained from participants and two industrial hygienists assigned exposures to 185 jobs using a checklist of 293 agents. Experts rated exposure for each job-agent combination according to exposure status (unexposed/exposed), confidence that the exposure occurred (possible/probable/definite), intensity (low/medium/high), and frequency (% time per week). The statistical unit of observation was each job-agent assessment (185 jobs × 293 agents = 54,205 assessments per expert). Crude agreement, Gwet AC1/2 statistics, and Cohen's Kappa were used to estimate inter-rater agreement for confidence and intensity; for frequency, the intra-class correlation coefficient (ICC) was used. The majority of job-agent combinations were evaluated by the two experts to be not exposed (crude agreement >98% of decisions). The degree of agreement between the experts for the confidence of exposure status was Gwet AC1/2 = 0.99 (95% CI: 0.99-0.99), and for intensity, a Gwet AC2 = 0.99 (95% CI: 0.99-0.99). For frequency, an ICC of 0.31 (95% CI: 0.26-0.35) was found. A sub-analysis restricted to job-agent combinations for which the two experts agreed on exposure status revealed a moderate agreement for confidence of exposure (Gwet AC2 = 0.66) and high agreement for intensity (Gwet AC2 = 0.96). For frequency, the ICC was 0.52 (95% CI: 0.47-0.57). A high level of inter-rater agreement was found for identifying exposures and for coding intensity, but agreement was lower for the coding of frequency of exposure.

Estimating the burden of lung cancer in Canada attributed to occupational radon exposure using a novel exposure assessment method

Objective

Exposure to radon causes lung cancer. The scope and impact of exposure among Canadian workers have not been assessed. Our study estimated occupational radon exposure in Canada and its associated lung cancer burden.

Methods

Exposed workers were identified among the working population during the risk exposure period (1961–2001) using data from the Canadian Census and Labour Force Survey. Exposure levels were assigned based on 12,865 workplace radon measurements for indoor workers and assumed to be 1800 mg/m³ for underground workers. Lung cancer risks were calculated using the Biological Effects of Ionizing Radiation (BEIR) VI exposure-age-concentration model. Population attributable fractions were calculated with Levin’s equation and applied to 2011 Canadian lung cancer statistics.

Results

Approximately 15.5 million Canadian workers were exposed to radon during the risk exposure period. 79% of exposed workers were exposed to radon levels < 50 Bq/m³ and 4.8% were exposed to levels > 150 Bq/m³. We estimated that 0.8% of lung cancers in Canada were attributable to occupational radon exposure, corresponding to approximately 188 incident lung cancers in 2011.

Conclusions

The lung cancer burden associated with occupational radon exposure in Canada is small, with the greatest burden occurring among those exposed to low levels of radon.

Surface contamination with ten antineoplastic drugs in 83 Canadian centers

PURPOSE

The aim of this study was to monitor environmental contamination by 10 antineoplastic drugs in Canadian oncology pharmacy and patient care areas. The secondary objective was to explore the impact of factors that may explain contamination.

METHODS

Twelve standardized sites were sampled in each center (six in the pharmacy and six in patient care areas). Each sample was prepared to allow quantification of seven antineoplastic drugs (cyclophosphamide, ifosfamide, methotrexate, cytarabine, gemcitabine, 5-fluorouracil, irinotecan) by UPLC-MS-MS. Docetaxel, paclitaxel and vinorelbine were also detected, but not quantified due to sensibility limitations. The impact of some factors was evaluated compared with a Kolmogorov-Smirnov test for independent samples.

RESULTS

Eighty-three Canadian centers were recruited in 2017. A total of 953 surfaces were sampled, 495 in pharmacy and 458 in patient care areas. Cyclophosphamide was most often found on surfaces (36% of samples positive, 75th percentile 0.0040 ng/cm²). The arm rest (81.7% of samples positive for at least one antineoplastic drug), the front grille inside the hood (78.3%) and the floor in front of the hood (61.4%) were more frequently contaminated. Centers who prepared more antineoplastic drugs per year had higher concentration on different surfaces ( p < 0.0001).

CONCLUSION

Despite growing awareness and implementation of new safe handling guidelines, healthcare centers' surfaces remain contaminated with traces of many antineoplastic drugs. The use of personal protective equipment remains indisputable. Performing an annual monitoring remains a good indicator to monitor trends over time and to compare with similar centers.

But other than mesothelioma? An estimate of the proportion of work-related cancers in Quebec

BACKGROUND

More than 30 exposures in the workplace are proven carcinogens. In the present study, we aimed to estimate the burden of occupational cancer in Quebec so as to increase awareness among stakeholders and to prioritize research activities.

METHODS

Work-attributable fractions-that is, the proportions of cancers attributable to work-as published in Finland and the United Kingdom were applied to Quebec 2002-2006 cancer incidence and mortality data to estimate the number of work-related cases for 28 cancer sites.

RESULTS

Overall, 6.0% of incident cancers (men: 9.1%; women: 2.7%) and 7.6% of cancer deaths (men: 11.8%; women: 2.8%) could be attributable to work, resulting annually in an average of 2160 new cancer diagnoses and 1190 cancer deaths in Quebec. Incident cancers of the lung, prostate, skin, bladder, and (female) breast were the most numerous; cancer sites resulting in more deaths were lung, (female) breast, and pleura. During the same period, compensation statistics reported annual averages of 94.3 incident cancers and 61.9 cancer deaths, mostly involving mesothelioma (64% of compensated incident cancers) and lung cancer (30% of compensated incident cancers).

CONCLUSIONS

Increased recognition of workplace cancers by all stakeholders, from workers and employers to treating physicians, will foster appropriate preventive measures for safer workplaces.

FGF receptor genes and breast cancer susceptibility: results from the Breast Cancer Association Consortium

BACKGROUND

Breast cancer is one of the most common malignancies in women. Genome-wide association studies have identified FGFR2 as a breast cancer susceptibility gene. Common variation in other fibroblast growth factor (FGF) receptors might also modify risk. We tested this hypothesis by studying genotyped single-nucleotide polymorphisms (SNPs) and imputed SNPs in FGFR1, FGFR3, FGFR4 and FGFRL1 in the Breast Cancer Association Consortium.

METHODS

Data were combined from 49 studies, including 53 835 cases and 50 156 controls, of which 89 050 (46 450 cases and 42 600 controls) were of European ancestry, 12 893 (6269 cases and 6624 controls) of Asian and 2048 (1116 cases and 932 controls) of African ancestry. Associations with risk of breast cancer, overall and by disease sub-type, were assessed using unconditional logistic regression.

RESULTS

Little evidence of association with breast cancer risk was observed for SNPs in the FGF receptor genes. The strongest evidence in European women was for rs743682 in FGFR3; the estimated per-allele odds ratio was 1.05 (95% confidence interval=1.02-1.09, P=0.0020), which is substantially lower than that observed for SNPs in FGFR2.

CONCLUSION

Our results suggest that common variants in the other FGF receptors are not associated with risk of breast cancer to the degree observed for FGFR2.

Occupational exposure to solvents and male infertility

OBJECTIVES

To determine whether, in a case-referent study of infertility patients, cases with low motile sperm count were more likely than referents to have had exposure to organic solvents.

METHODS

Occupations of men attending fertility clinics in Canada were assigned codes reflecting probable exposure to organic solvents, at four grades of intensity, using a job exposure matrix previously developed. A case referent design was used, with cases being defined as men with <12x10(6)/ml motile sperm. Information from 656 men in manual work attending a single clinic in Montreal in 1972-91 was used for the main study. A separate analysis was conducted with information for 574 men in manual work attending 10 further clinics across Canada in 1984-7.

RESULTS

In the Montreal series a significant association was found between intensity of exposure to solvents and clinical findings of <12x10(6)/ml motile sperm. Odds ratios (ORs), after allowing for confounding, were 2.07 (95% confidence interval (95% CI) 1.24 to 3.44) for moderate exposure to solvents and 3.83 (95% CI 1.37 to 10.65) for high exposure. In the second series of 568 men, the effect was confirmed at high exposure to solvents (OR 2.90, 95% CI 1.01 to 8.34) but not at moderate exposure (OR 1.01, 95% CI 0.53 to 1.92).

CONCLUSIONS

Exposure to organic solvents is common both at work and in recreational pursuits. The results of this study suggest that efforts should be made to identify the compounds hazardous to male fertility, and if the risk is confirmed, to regulate their use.

Occupational risk factors for female breast cancer: a review

OBJECTIVES

Although progress has been made in identifying personal risk factors and in improving treatment for female breast cancer, incidence rates continue to increase. With women now occupying a sizable fraction of the workforce, it is worth inquiring whether there are occupational risk factors for breast cancer. This is a review of occupational studies on female breast cancer.

METHODS

Suitable reports and published articles with associations of female breast cancer and occupation were identified from technical reports, by searching the MEDLINE bibliographic data base, and by reviewing each paper on cancer that was published in 20 major journals during the period from about 1971-94.

RESULTS

A total of 115 studies were identified; 19 studies relied exclusively on data collected for administrative purposes, and there were four incident case-control studies and 92 cohort studies. Although data for individual industries, occupations, and exposures were sparse, there was limited evidence of an association with employment in the pharmaceutical industry and among cosmetologists and beauticians. Associations were also found for chemists and occupations with possible exposure to extremely low frequency electromagnetic fields, but potential methodological weaknesses preclude drawing any definite conclusions. There was little support for increased risks among textiles workers, dry cleaning workers, and nuclear industry workers.

CONCLUSIONS

Few high quality occupational studies directed specifically toward women have been carried out to allow the unambiguous identification of occupational risk factors for breast cancer. It is suggested that investigations that account for non-occupational risk factors and that assess exposure in a more detailed way be carried out. One strategy already suggested is to conduct population based, case-control studies in which subjects are interviewed about their occupational histories and exposure to chemical and physical agents which are then attributed from the job descriptions by a team of experts. These studies can then be supplemented when necessary with cohort studies of specific populations.

Relationships between three indicators of lead exposure in workers: blood lead, delta-aminolevulinic acid and free erythrocyte protoporphyrin

Whole blood lead (Pb-B), urinary delta-aminolevulinic acid (ALA-U) and free erythrocyte protoporphyrin (FEP) were measured in three groups of workers (n = 196) with different degrees of exposure to lead, and one group of men with no previous exposure to the metal (n = 48). Inter-group comparison showed a correlation of r = 0.73 between Pb-B and log of ALA-U, and r = 0.91 between Pb-B and log of FEP. ALA-U and FEP values rose sharply after Pb-B values reached 450-500 micrograms/l.