An analysis of the risk of B-lymphocyte malignancies in industrial cohorts

Systematic Review and Meta-Analysis of Selected Cancers in Petroleum Refinery Workers

OBJECTIVE

We studied the risk of 11 cancers of a priori interest in petroleum refinery workers.

METHODS

Iterative searches identified 36 studies for the 11 cancer sites. Statistical heterogeneity and publication bias were assessed to enhance interpretation of meta-relative risks.

RESULTS

Statistical heterogeneity was marked for mesothelioma, but was largely due to study quality. Higher quality studies showed a meta-relative risk (RR) of 3.22, (95% prediction interval 1.45 to 7.23). Melanoma (meta-RR = 1.23) and acute lymphoid leukemia (meta-RR = 1.51), showed results consistent with higher risk, but both were driven by one or two studies. Eight other cancer outcomes showed summary meta-RR's consistent with unity.

CONCLUSIONS

Most cancer outcomes are consistent with background risk in refinery workers. This work has clarified an excess mesothelioma risk, conditional on study quality stratification. Continued surveillance is warranted for melanoma and ALL.

Acute myeloid and chronic lymphoid leukaemias and exposure to low-level benzene among petroleum workers

BACKGROUND

High benzene exposure causes acute myeloid leukaemia (AML). Three petroleum case-control studies identified 60 cases (241 matched controls) for AML and 80 cases (345 matched controls) for chronic lymphoid leukaemia (CLL).

METHODS

Cases were classified and scored regarding uncertainty by two haematologists using available diagnostic information. Blinded quantitative benzene exposure assessment used work histories and exposure measurements adjusted for era-specific circumstances. Statistical analyses included conditional logistic regression and penalised smoothing splines.

RESULTS

Benzene exposures were much lower than previous studies. Categorical analyses showed increased ORs for AML with several exposure metrics, although patterns were unclear; neither continuous exposure metrics nor spline analyses gave increased risks. ORs were highest in terminal workers, particularly for Tanker Drivers. No relationship was found between benzene exposure and risk of CLL, although the Australian study showed increased risks in refinery workers.

CONCLUSION

Overall, this study does not persuasively demonstrate a risk between benzene and AML. A previously reported strong relationship between myelodysplastic syndrome (MDS) (potentially previously reported as AML) at our study's low benzene levels suggests that MDS may be the more relevant health risk for lower exposure. Higher CLL risks in refinery workers may be due to more diverse exposures than benzene alone.

MTHFR C677 T gene polymorphism in lymphoproliferative diseases

Methylenetetrahydrofolate reductase (MTHFR), a key enzyme in folate metabolism, has been implicated in cancer risk. In the present study we used a melting curve analysis to investigate the association of the common MTHFR C677 T polymorphism with lymphoproliferative diseases. Patients (n=117) were compared with age- and sex-matched control subjects (n=154). Our results indicate that the 677 T variant occurred less frequently in patients (26%) than in the control group (33.7%; P=0.05). Investigation of the variant allele (677 T) frequency in the subgroups with Hodgkin's lymphoma (HL) and B-cell neoplasms (BCNs) revealed that this difference was a result of the significantly lower distribution of the variant allele in patients with HL (20.5%; P=0.01). This was accompanied by a significantly higher frequency of the homozygote normal genotype (677CC) among the patients with HL. In patients with BCNs the distribution of the variant allele (30.3%) was comparable to that in the control group (P=0.47). However, the difference between HL (20.5%) and BCNs (30.3%) did not reach statistical significance (P=0.09). Our results suggest that the distribution of the C677 T polymorphism may vary among lymphoproliferative diseases.

Update: cohort mortality study of workers highly exposed to polychlorinated biphenyls (PCBs) during the manufacture of electrical capacitors, 1940-1998

BACKGROUND

The National Institute for Occupational Safety and Health previously reported mortality for a cohort of workers considered highly exposed to polychlorinated biphenyls (PCBs) between 1939 and 1977 at two electrical capacitor manufacturing plants. The current study updated vital status, examined liver and rectal cancer mortality previously reported in excess in this cohort and evaluated mortality from non-Hodgkin's lymphoma (NHL) and cancers of the stomach, intestine, breast, prostate, skin (melanoma) and brain reported to be in excess in other cohort and case-control studies of PCB-exposed persons.

METHODS

Mortality was updated through 1998 for 2572 workers. Age-, gender-, race- and calendar year-adjusted standardized mortality ratios (SMRs) and 95% confidence intervals (CI) were calculated using U.S., state and county referent rates. SMRs using U.S. referent rates are reported. Duration of employment was used as a surrogate for exposure.

RESULTS

Consistent with the previous follow-up, mortality from biliary passage, liver and gall bladder cancer was significantly elevated (11 deaths, SMR 2.11, CI 1.05 - 3.77), but mortality from rectal cancer was not (6 deaths, SMR 1.47, CI 0.54 - 3.21). Among women, mortality from intestinal cancer (24 deaths, SMR 1.89, CI 1.21 - 2.82) and from "other diseases of the nervous system and sense organs", which include Parkinson's disease and amyotrophic lateral sclerosis, (15 deaths, SMR 2.07, CI 1.16 - 3.42) were elevated. There were four ALS deaths, all women (SMR 4.35, CI 1.19-11.14). Mortality was elevated for myeloma (7 deaths, SMR 2.11, CI 0.84 - 4.34), particularly among workers employed 10 years or more (5 deaths, SMR 2.80, CI 0.91 - 6.54). No linear associations between mortality and duration of employment were observed for the cancers of interest.

CONCLUSION

This update found that the earlier reported excess in this cohort for biliary, liver and gall bladder cancer persisted with longer follow-up. Excess mortality for intestinal cancer among women was elevated across categories of duration of employment; myeloma mortality was highest among those working 10 years or more. The small numbers of deaths from liver and intestinal cancers, myeloma and nervous system diseases coupled with the lack of an exposure-response relationship with duration of employment preclude drawing definitive conclusions regarding PCB exposure and these causes of death.

Occupational exposures and haematological malignancies: overview on human recent data

OBJECTIVE

Occupational causes of haematological malignancies are relatively uncommon, under-studied and under-identified. They are also often unrecognized by clinicians. This review summarizes the principal epidemiologic studies on this topic.

METHODS

We analyzed the recent relevant human data found in the Medline, the Pascal and the BDSP databases.

RESULTS

Benzene and ionizing radiation are the only agents conclusively demonstrated to be carcinogenic to the haematopoietic system. In particular, both exposures are strongly associated with acute myeloid leukaemia. Low doses of both may also be related to myeloid malignancies. Infectious agents and pesticides are also thought to induce lymphoproliferative cancers. Some studies show an association between haematological malignancies and low-frequency electromagnetic fields and organic solvents. All of these suspected occupational causes must be confirmed by further studies.

CONCLUSIONS

Better knowledge and understanding of occupational causes of haematological malignancies are necessary to improve their prevention and compensation.

Childhood cancers and atmospheric carcinogens

STUDY OBJECTIVES

To retest previous findings that childhood cancers are probably initiated by prenatal exposures to combustion process gases and to volatile organic compounds (VOCs); and to identify specific chemical hazards.

DESIGN

Birth and death addresses of fatal child cancers in Great Britain between 1966 and 1980, were linked with high local atmospheric emissions of different chemical species. Among migrant children, distances from each address to the nearest emissions "hotspot" were compared. Excesses of outward over inward migrations show an increased prenatal or early infancy risk.

SETTING AND SUBJECTS

Maps of emissions of many different substances were published on the internet by the National Atmospheric Emissions Inventory and "hotspots" for 2001 were translated to map coordinates. Child cancer addresses were extracted from an earlier inquiry into the carcinogenic effects of obstetric radiographs; and their postcodes translated to map references.

MAIN RESULTS

Significant birth proximity relative risks were found within 1.0 km of hotspots for carbon monoxide, PM10 particles, VOCs, nitrogen oxides, benzene, dioxins, 1,3-butadiene, and benz(a)pyrene. Calculated attributable risks showed that most child cancers and leukaemias are probably initiated by such exposures.

CONCLUSIONS

Reported associations of cancer birth places with sites of industrial combustion, VOCs uses, and associated engine exhausts, are confirmed. Newly identified specific hazards include the known carcinogens 1,3-butadiene, dioxins, and benz(a)pyrene. The mother probably inhales these or related materials and passes them to the fetus across the placenta.