Cancer incidence among laboratory workers in biomedical research and routine laboratories in Israel: Part II-nested case-control study

BACKGROUND: A case-control study nested within a cohort study of biomedical laboratory workers was conducted to examine whether the excess cancer morbidity that we found can be explained by exposure to a particular group of substances, taking into consideration potential confounders. METHODS: The study population included 163 cases and two matched control groups: laboratory workers (311) and general population (448) workers. RESULTS: Multiple conditional regression analysis showed that working in research laboratories involved an increased risk of cancer generally among women [risk ratio 2.2 (1.2-4.3)], and of breast cancer particularly [risk ratio 2.3 (1.1-4.7). Seventy-six percent (76%) of breast, 87% of thyroid, 60% of ovary and prostate, 94% of melanoma, and 50% of leukemia cases were ever exposed to at least one known human carcinogen. CONCLUSION: Our results exclude the possibility that the excess cancer morbidity was related to personal risk factors but they may be explained by exposure factors. Am. J. Ind. Med. 44:611-626, 2003.     

Exposure to chemical carcinogens and risk of cancer among Finnish laboratory workers

BACKGROUND: Laboratory workers have long been suspected of having increased risks of cancer due to their occupation. We evaluated occupational exposure and cancer incidence among Finnish laboratory workers. MATERIALS AND METHODS: The cohort was comprised of 4,722 laboratory workers reported to the Finnish Register of Workers Exposed to Carcinogens in 1979-1988. The standardized incidence ratios (SIR) for cancers and their 95% confidence intervals (CI) were calculated based on data of the Finnish Cancer Registry. RESULTS: The most common carcinogens, to which these workers were potentially exposed, were chromium (VI), carbon tetrachloride, cadmium, benzene, and chloroform. From this cohort, 174 persons were recorded with primary tumors in 1980-1999. The SIR for cancer of all sites combined was 0.99 (CI 0.85-1.14). None of the cancer-specific SIRs were significantly elevated. Slight excesses were found, e.g., for non-Hodgkin's lymphoma (seven observed, 4.8 expected) and leukemia (four observed, three expected). CONCLUSIONS: This study did not suggest any major cancer risks among Finnish laboratory workers but the follow-up time of the cohort was too short (on an average 15.7 years) to reveal possible cancer risks requiring a longer induction period.     

Cancers in concrete workers: results of a cohort study of 33,668 workers

OBJECTIVES—To study cancer morbidity patterns in concrete workers.
METHODS—A cohort of 33 503 concrete workers was enrolled in the study from 1971-86. The average duration of follow up was 19.4 years (582 225 person-years). The workers' cancer morbidity was compared with the morbidity of the general population.
RESULTS—A total of 3572 incident cancers were observed. Significantly increased standardised incidence ratios (SIRs) were found for all malignant neoplasms (SIR 107; 95% confidence interval (95%CI) 103 to 110), cancer of the lip (SIR 179; 95%CI 134 to 234), cancer of the stomach (SIR 139; 95%CI 122 to 158), cancer of the lung (SIR 125; 95%CI 114 to 137), and cancer of the prostate (SIR 108; 95%CI 101 to 116). Reduced risk was found for cancer of the large intestine (SIR 80; 95%CI 69 to 93) and cancer of the testis (SIR 50; 95%CI 26 to 87). Smoking was more prevalent among the concrete workers than in the general population (50% v 35%).
CONCLUSION—The study has shown a slightly increased overall risk of cancer among concrete workers. The increased risk of lung cancer could entirely be due to differences in smoking habits between concrete workers and the general population. There is a possibility that the smoking also has contributed to the increased risks of stomach cancer and lip cancer, but occupational factors may have contributed to these cancer sites.


Keywords: occupational diseases; constructions workers; smoking     

Cancer incidence and mortality in workers employed at a transformer manufacturing plant: update to a cohort study

BACKGROUND: This study is an extension of a previously published analysis of cancer mortality in a transformer manufacturing plant where there had been extensive use of mineral oil transformer fluid. The objectives of the present study were to update the mortality analysis and include deaths for the past 6 years as well as to do an analysis of cancer incidence of the cohort. METHODS: A cohort of 2,222 males working at a transformer manufacturing plant between 1946 and 1975 was constructed. Using a classical historical cohort study design, cancer incidence and mortality were determined through record linkage with Canadian provincial and national registries. The rates of cancer incidence and mortality experienced by this cohort were compared to that of the Canadian male population. RESULTS: A statistically significant increased risk of developing and dying of pancreatic cancer was found but not an increase in overall cancer mortality. This was consistent with the previous report from this group. Interestingly, the cohort demonstrated a statistically significant risk of overall cancer incidence and specific increased incidence of gallbladder cancer. CONCLUSIONS: This study contributes further evidence to the growing body of literature indicating the carcinogenic properties of mineral oils used in occupational settings, in particular those used prior to 1970s.     

A cohort study on cancer incidence among Danish gardeners.

This study was performed to examine the cancer risk of Danish gardeners having been highly exposed to pesticides. We have followed a cohort of 4,015 employed gardeners (859 females and 3,156 males) from May 1975 until the end of 1984 with regard to cancer incidence. The observed incidence was compared with expected numbers calculated from national incidence rates. For all cancer sites combined, the standardized morbidity ratio (SMbR) was 104. Among male gardeners a significantly increased incidence was seen for soft tissue sarcoma (SMbR = 526, 95% confidence interval (CI): 109-1,538), an chronic lymphatic leukemia (SMbR = 275, 95% CI: 101-599). The incidence of non-Hodgkin's lymphoma was twice that which was expected (SMbR = 200, 95% CI: 86-393). We suggest that some of the pesticides to which the gardeners have been exposed are capable of initiating or promoting the development of malignant neoplasms in tissues of mesenchymal origin.     

Cancer in ex‐asbestos cement workers in Israel, 1953–1992

A cohort of 3,057 male workers employed in an asbestos‐cement plant using 90% chrysotile‐10% crocidolite, located in Northern Israel, was followed from 1953–1992 for incidence and mortality from cancer. In the years 1978–1992, the cohort had an elevated risk for all malignant neoplasms combined (n > 153, SIR > 117, ns), lung cancer (n > 28, SIR > 135, ns), mesothelioma (n > 21; SIR >5000, p > .0001), unspecified pleural cancer (n > 5; SIR > 278 , P > .0001), and liver cancer (n > 7, SIR 290, ns). Risks for colo‐rectal (n > 19; SIR > 79, ns), bladder (n = 12, SIR 69) and renal cancers (n > 5, SIR 104) were less than expected. Risk for mesothelioma showed a sharp risk gradient with duration of exposure, increasing from 1 per 625 for those employed less than 2 years to 1 per 4.5 workers employed over 30 years. The ratio of mesothelioma to excess lung cancer cases was 2.9 to 1, or 3.6 to 1, if pleural cases of unspecified origin were included; the pleura to peritoneum ratio of verified mesothelioma cases was 20 to 1. This atypically high ratio of mesothelioma to excess lung cancer cases is suggested to be the combined result of high past asbestos exposures in the workers and their low prior risk for lung cancer, and possibly, relatively early smoking cessation in relation to asbestos exposure. Am. J. Ind. Med. 35:1–8, 1999. © 1999 Wiley‐Liss, Inc.     

Mortality and cancer incidence among PVC-processing workers in Sweden

The mortality pattern and the cancer incidence were investigated among 717 men who had been employed for at least 3 months during 1964–1974 in three Swedish PVC-processing plants. The mortality was followed 1964–1986 and the cancer incidence 1964–1984. Expected figures were calculated from Swedish national rates. Among Swedish citizens, the observed mortality and cancer incidence was close to the expected in most diagnoses. Among immigrants, mostly from Finland, there was a marked excess of circulatory deaths. This finding was probably due to the higher incidence of coronary mortality in Finland compared to Sweden. In the whole cohort, five cases of malignant melanoma had occurred as compared to 1.5 expected (SMR = 3.4, 95% confidence limit 1.1–7.9). This may be due to chance but merits further investigation since an increased incidence of malignant melanoma has previously been found among Norwegian PVC-manufacturing workers. © 1993 Wiley-Liss, Inc.     

Texaco mortality study: III. A cohort study of producing and pipeline workers

While there have been numerous epidemiology studies of refinery workers, no studies have been done on producing and pipeline workers. This is a retrospective follow-up study of all persons who were employed for at least 6 months at a Texaco producing or pipeline location and who worked at some time during the period 1946-1980. Of the 11,098 white men in the cohort, 8,964 were alive, 1,886 were known to be dead, and the vital status of the remaining 248 as of December 31, 1980 was unknown. The standardized mortality ratio (SMR) of 63 for all causes was significantly low, on the basis of 2,976 expected deaths. Statistically significant deficits also were seen for all major causes of death. Mortality patterns were also examined for the major job categories in these departments. Similar patterns of mortality were seen, although there was a significant excess of thyroid cancer in those employed as pumper-gaugers. However, it was based on only four cases.     

Mortality among workers at municipal waste incinerators in Rome: A retrospective cohort study

A retrospective mortality study of a cohort of 532 male subjects employed at two municipal plants for garbage recycling and incinerating has been conducted. All workers ever employed at the plants since 1962 were enrolled and followed up from January 1, 1965 to December 31, 1992. Standardized Mortality Ratios (SMRs) and 90% confidence intervals (90%CI) were calculated using regional population mortality rates. The study yielded a total of 8,585 person-years of observation. Mortality from all causes was significantly lower than expected (observed [obs] = 31; SMR = 0.71; 90%CI = 0.51–0.95). All cancer mortality was comparable with that of the general population (obs = 15; SMR = 0.95; 90%CI = 0.58–1.46). Mortality from lung cancer was reduced (obs = 3; SMR = 0.55; 90%CI = 0.15–1.42). Increased risk was found for gastric cancer (obs = 4; SMR = 2.79: 90%CI = 0.94–6.35). Analysis by latency indicated that the excess risk of gastric cancer was confined in the category with more than 10 years since first exposure. Our results for gastric and lung cancers indicate the need to further investigate the role on cancer of occupational exposure to organic dust and bacterial endotoxins in the waste management. Am. J. Ind. Med. 31:659–661, 1997. © 1997 Wiley-Liss, Inc.     

Cancer mortality and incidence among a cohort of benzidine and dichlorobenzidine dye manufacturing workers

BACKGROUND: Benzidine is classified as a definite human carcinogen and dichlorobenzidine as a probable human carcinogen. METHODS: A cohort study of 538 workers potentially exposed to benzidine and/or dichlorobenzidine from a single chemical manufacturing facility was conducted. Social Security records were used to identify all employees who worked at the facility from 1960 to 1977. Vital status was determined through 2001 and cancer incidence through 2002. RESULTS: A total of 22 bladder cancer cases were identified. For three individuals, bladder cancer was the underlying cause of death. Increased standardized mortality ratios (SMRs) were found for all cancer 1.54 (95% CI 1.04-2.19), bladder cancer 8.34 (95% CI 1.72-24.78), and lymphohematopoietic cancer 2.84 (95% CI 1.04-6.18). The standardized incidence ratio (SIR) for bladder cancer was 6.85 (95% CI 4.30-10.4). Only one case of bladder cancer was identified among the workers who were exposed to dichlorobenzidine only. However, an increased risk for lymphohematopoietic cancer was found among these dichlorobenzidine only workers (SMR 6.62 (95% CI 1.37-19.36)). CONCLUSIONS: This study confirms the high risk of bladder cancer among benzidine exposed workers even years after exposure has ceased, and raises suggestive evidence of increased risk to lymphohematopoietic cancer from exposure to benzidine or dichlorobenzidine.     

Assessment of cancer clusters using limited cohort data with spreadsheets: Application to a leukemia cluster among rubber workers

This paper presents methods for initial investigation of occupational cancer clusters using limited data. Phase 1 of the methods developed uses basic data from the cluster of cases, but with cohort data limited to the size of the workforce at the plant. Phase 2 of the methods requires knowledge of the number of workers entering and leaving the workforce in each year. In the absence of data concerning age, the spreadsheet programs explore a variety of worker age distributions in synthetic cohort analyses. The methods were used to assess a cluster of six cases of leukemia with an average duration of work of 11 years in a tire manufacturing plant. It was concluded that the relative risk for the age range 30-50 was at least 7, providing further evidence for the association of leukemia with work in tire manufacture. The use of spreadsheet programs can provide a valuable first step assessment of apparent workplace cancer clusters.     

Cohort study among workers exposed to benzene in China: I. General methods and resources

Benzene is recognized internationally as a leukemogen, but the available data to clarify dose-response relationships and examine risks of malignancies other than leukemia are sparse. A collaborative study was therefore carried out to expand on a previous retrospective cohort mortality study of Chinese benzene-exposed workers. Methods and resources used in the 16-year follow-up of 74,828 benzene-exposed and 35,805 unex-posed workers employed for any length of time during 1972–1987 in 712 factories in 12 cities in China are described. Details are provided of the study organization, assessment of benzene exposures since 1949, characterization of factories and workers by exposure status, city, and sex, identification and confirmation of cancers and other deaths, and quality control procedures. The distinguishing features of the study are discussed in relation to earlier cohort studies, and study limitations as well as strengths are presented.     

A case-control study of employment experience and lung cancer among rubber workers

In this case-control study the detailed employment histories of 121 rubber plant employees who died of lung cancer from 1964 through 1973 were compared to those of 448 plant employees (controls) who died of other causes during the same calendar period. All subjects were white male hourly employees. Lung cancer cases and controls were matched individually on year of birth and year of first hire at the plant. Results of matched analyses indicated that there was no association between lung cancer mortality and employment in either rubber compounding and mixing jobs or curing jobs. Men who had worked for at least five years in rubber reclaim operations, where there was potentially heavy exposure to particulates and fumes, experienced a twofold increase in lung cancer risk. In addition, there was a 70% excess of lung cancer risk among men employed in making special products, where the primary production activity was fuel cell manufacturing. The latter two findings were marginally statistically significant.     

Leukemia in relation to occupational exposures to benzene and other agents: a case-control study nested in a cohort of gas and electric utility workers

BACKGROUND: Many occupational and environmental exposures have been implicated in the etiology of leukemia, but only a few, such as benzene, are well-established leukemogens. The risk of leukemia in a large cohort of gas and electricity utility workers with exposures to several suspected or confirmed carcinogens was investigated. METHODS: A case-control study nested within the cohort was conducted, with 72 leukemia cases identified among male workers, and 285 controls matched to the cases by year of birth. Only cases, and their matched controls, active in the company at the date of diagnosis were included. Exposure assessment was based on a job-exposure matrix (JEM) developed from expert judgment using a standardized procedure. RESULTS: The risk of leukemia was increased in workers with an estimated cumulative exposure to benzene > or = 16.8 ppm-years (OR = 3.6; 95% CI 1.1-11.7), and there was an indication of a dose-response relation (OR = 1.2; 95% CI 1.0-1.5 per 10 ppm-years increase in exposure). The link with benzene was more pronounced for acute leukemia than for chronic leukemia, but no association with a particular leukemia cell type was apparent. The risk of leukemia remained elevated for latency periods of 2, 5, or 10 years. CONCLUSIONS: From our evaluation, it could be estimated that the median TWA exposure to benzene among exposed workers was 0.16 ppm, i.e., within concentration ranges where an increased leukemia risk was usually not apparent in previous epidemiological studies. Although an increased leukemia risk may be real, it may also be related to other occupational factors not totally controlled for in the analysis, or to benzene exposures actually higher than expected.     

Cohort study on cancer mortality among workers in the pulp and paper industry in Catalonia,Spain

We examined mortality in a retrospective follow-up study of 3,241 workers employed between 1970–1992, in four pulp and paper mills in Catalonia, Spain. Vital status was determined for 95% of the cohort. Exposure was reconstructed using job histories and a company exposure questionnaire. Standardized mortality ratios (SMR) were derived using mortality rates of Spain as the reference. For all workers, mortality from all causes (SMR = 76; 95%; confidence intervals [CI] = 65–88; 189 deaths) and all malignant neoplasms (SMR = 93; CI = 72–119; 65 deaths) were less than the expected. Excess risk was observed for mortality from all neoplasms in females (SMR = 168; CI 84–303; 11 deaths), for large intestine cancer in both sexes (SMR = 250; CI = 115–525; 8 deaths), particularly after 10 years of employment and latency (SMR = 355; CI = 154–701; 8 deaths), and for breast cancer in females (SMR = 286; CI = 77–732; 4 deaths). These findings suggest that workers employed in the pulp and paper industry may have an excess risk of specific cancers. © 1996 Wiley-Liss, Inc.