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Occupational Medicine Advance Access originally published online on January 16, 2007
Occupational Medicine 2007 57(3):186-190; doi:10.1093/occmed/kql171
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© The Author 2007. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

A cohort mortality and cancer incidence survey of recent entrants (1982–91) to the UK rubber industry: findings for 1983–2004

Abid Dost1, JK Straughan2 and Tom Sorahan3

1 British Tyre Manufacturers' Association Limited, 6 Bath Place, Rivington Street, London EC2A 3JE, UK
2 Occupational Health and Screening Services, Cleeton Court, Cleeton St Mary, Kidderminster, Worcestershire DY14 0QZ, UK
3 Institute of Occupational and Environmental Medicine, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Correspondence to: Abid Dost, British Tyre Manufacturers' Association Ltd, 6 Bath Place, Rivington Street, London EC2A 3JE, UK. Tel: +44 20 7457 5040; fax: +44 20 7972 9008; e-mail: adost{at}btmauk.com


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
 References
 
Aim To monitor the occurrence of cancer in a recently defined cohort of UK rubber workers.

Methods A cohort of 8651 male and female workers from 41 UK rubber factories has been enumerated. All employees had a minimum of 12 months employment and were first employed at one of the participating factories in the period 1982–91. Mortality and cancer incidence data for the period 1983–2004 were compared with expected values based on appropriate national rates.

Results Mortality from lung cancer was close to expectation for males [observed 22, standardized mortality ratio (SMR) 93] and females (observed 2, SMR 70). Mortality from stomach cancer was also unexceptional in males (observed 4, SMR 86) and females (observed 0, SMR 0). Although based on small numbers, significantly elevated mortality was shown for multiple myeloma in males (observed 5, SMR 385) and females (observed 2, SMR 952). All seven of these latter deaths occurred in workers from the general rubber goods (GRG) sector.

Conclusions The findings should be treated with caution as they relate to a relatively early period of follow-up. Nevertheless, they hold out the prospect that the elevated SMRs for stomach and lung cancers reported for historical cohorts of UK rubber workers will not be present in more recent cohorts. The elevated occurrence of multiple myeloma may represent no more than a chance finding. Alternatively, these findings may reflect the presence of an unrecognized occupational cancer hazard in parts of the GRG sector of the UK rubber industry.

Keywords      Cohort study; lung cancer; multiple myeloma; rubber workers; stomach cancer


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Conflicts of interest
 References
 
The evidence of a carcinogenic risk in the rubber industry was last reviewed in detail by the International Agency for Research on Cancer in 1982 [1]. More recently published epidemiological studies concerning the rubber industry have been reviewed by Kogevinas et al. [2], and their likely relevance to the current UK industry has been commented upon [3,4]. Rubber industry work was highlighted as a possible cause of prostate cancer in a recent literature review of occupation and prostate cancer risks [5], although two large UK studies that found no excess of prostate cancer were ignored [6,7]. Following the Kogevinas review, studies of cancer risks in German [8–11], Polish [12] and UK rubber workers [13–15] have been published, although only one of these studies is concerned with rubber workers first employed in recent decades [15].

The present study [15] was initiated in the 1980s and for two main reasons; firstly, to determine whether or not the improvements in working conditions introduced in the UK rubber industry have been accompanied by an elimination of concerns relating to occupational lung and stomach cancers in this industry [6,7] and secondly, to provide an early warning of any new serious health problems.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Conflicts of interest
 References
 
A total of 41 rubber factories from England and Wales (n = 37) and from Scotland (n = 4), all members of the former British Rubber Manufacturers' Association (BRMA), supplied identifying particulars, work histories and smoking status information for all those 7561 male and 1090 female workers first employed in the factory environment of the participating facilities during the 10-year period 1982–91. Office workers are thus excluded whereas maintenance workers are included in the cohort. [There are now two trade associations representing the UK rubber industry: the British Tyre Manufacturers' Association represents the tyre industry and the British Rubber and Polyurethane Products Association (BRPPA) represents the general rubber goods (GRG) sector.] All study subjects were employed for a minimum period of 12 months. Each period of working has been classified by principal industry sector (tyre, GRG) and by one of 12 broad BRMA job types (e.g. ‘curing or vulcanizing’, ‘component building and assembly’). Information on cigarette smoking at the time of hire was available for 4821 study subjects, but only in terms of current smoker (n = 2108), ex-smoker (n = 372) and lifelong non-smoker (n = 2341).

The Office for National Statistics (ONS) provided information on the vital status of each study subject up to the current closing date of the survey (31 December 2004): 8130 (94.0%) subjects were alive, 61 (0.7%) subjects had emigrated, 301 (3.5%) were deceased and 159 (1.8%) subjects were untraced. (‘Flagging’ is not available in Northern Ireland, and 380 workers from a further factory from Northern Ireland are not included in the present analysis. The experience of these workers will be included in the next update using the ‘one-off tracing’ that is available in Northern Ireland. The main study file also includes 330 workers from seven BRPPA member companies engaged in the manufacture of polymers from 4,4'-methylene-bis-ortho-chloroaniline; findings for this sub-cohort will be provided separately at a later date.) The underlying cause of death was coded according to the contemporaneous revision of the International Classification of Diseases. The ONS also supplied information on cancer registrations (incident cancers) for the period 1983–2004. Initially, there were 20 deaths from cancer with no corresponding cancer registration particulars. Requests for further assistance were made to the ONS to locate these ‘missing’ cancer registrations and all but four registrations were identified.

Expected numbers of deaths were calculated by applying sex-, age- and period-specific mortality rates for England and Wales and rates for Scotland to corresponding person-years-at-risk (PYR) for workers from factories in England and Wales and Scotland, respectively. Each study subject contributed PYR from the end of the first 12 months of employment to the closing date of the study, death, emigration or date last known alive, whichever was the earliest. Standardized mortality ratios (SMRs) were calculated as the ratio of observed deaths to expected deaths, expressed as a percentage. These procedures were carried out using the PERSONYEARS programme. Standardized registration ratios (SRRs) were calculated in the same way for the cancer morbidity data, except that incidence rates for England and Wales were applied to the total cohort. The mean age at commencing employment was 28.5 years (males 28.1 years, females 30.7 years) and follow-up ranged from 1 to 23 years (males: mean 17.6 years, median 17.6 years; females: mean 17.8 years, median 18.1 years).


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Conflicts of interest
 References
 
Observed and expected numbers of deaths and cancer registrations are shown in Table 1 for most sites of cancer, together with observed and expected numbers of deaths for the larger non-cancer groupings. Marked deficits in mortality are shown in male workers for diseases of the circulatory system, suicide and all causes. The only significant excesses shown for mortality are those for multiple myeloma in males (SMR 385, Obs 5) and females (SMR 952, Obs 2). There was also a significant excess incidence of multiple myeloma in females (SMR 811, Obs 3). There was no elevated mortality from stomach or lung cancer in males or females although a non-significant excess incidence of stomach cancer is shown in males (SRR 137, Obs 10).


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  		Table 1. Overall findings from BRMA Health Research Project II (7561 males and 1090 females) first employed in the UK rubber industry in the period 1982–91

 
Mortality (males and females combined) from stomach cancer, lung cancer, multiple myeloma and all causes are shown by period from commencing employment in Table 2. A significant positive trend is shown only for all causes mortality (P < 0.001), indicating the presence of a strong healthy worker effect in the data. Corresponding findings by industry sector are shown in Table 3. The excess mortality from multiple myeloma was found to be limited to the GRG sector (SMR 714, Obs 7). There is also a highly significant deficit from all causes mortality in tyre sector workers (SMR 55, Obs 99). Analyses were also carried out by first job. Numbers were too small for meaningful statistical interpretation although three of the seven deaths from multiple myeloma had been first employed in curing or vulcanizing.


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  		Table 2. Mortalitya from selected causes by period from hire, 1983–2004

 

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  		Table 3. Mortalitya from selected causes by industry sector, 1983–2004

 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Conflicts of interest
 References
 
There was an excess occurrence of multiple myeloma in this study although it is not usually possible to interpret findings based on small numbers with any confidence. There were five deaths from multiple myeloma in males but only three corresponding cancer registrations. This was because one of the deaths was recorded in the national cancer registration system as a ‘secondary malignant neoplasm of bone and bone marrow’. It is thus at least possible that one of the multiple myeloma deaths has been incorrectly assigned on the death certificate. In addition, while one of the other multiple myeloma deaths occurred 8 years after commencing employment, the original cancer was diagnosed within 12 months of hire (i.e. before completing the minimum period of employment for entry to the study) and was thus not included in the incidence findings. It would seem very unlikely that this case could be occupational in origin. Nevertheless, taken together (males and females, mortality and incidence), the findings for multiple myeloma are a cause for possible concern. The earlier larger BRMA study of UK rubber workers found deficits for multiple myeloma for all three follow-up periods [6,16,17]. However, this latter study was dominated by the tyre sector and these reassuring results may not be so relevant to the current concern, an excess of multiple myeloma in the GRG sector. Further epidemiological investigations of multiple myeloma risks may benefit from occupational hygiene and toxicological insights into exposures present in the recent UK rubber industry, particularly the GRG sector.

This study of recent entrants to the UK industry, whist still at a relatively early stage of follow-up, indicates, however, that overall health, as judged by mortality from all causes and all cancers, is better than the national average. The findings for stomach and lung cancer will also continue to be welcome news for UK rubber workers and are consistent with the time trends of decreasing exposure to rubber dust and fume in the UK rubber industry [18]. At this stage of follow-up, however, it is only possible to conclude that there is no discernible evidence of late-stage lung and stomach carcinogens in the industry.

An elevated mortality from cancer of the testes (based on three deaths) was highlighted in the earlier report from this study [15]. There were, however, no further deaths from this cancer in the new period of follow-up (1999–2004) and the incidence of testicular cancer is now below expectation. There is, therefore, no reason to believe that working in the UK rubber industry has an effect on risks for this cancer.

In the course of time, there will be a sufficient number of events in this new cohort study to make use of the detailed work history information and the smoking status information in a single analysis of the various cancers under investigation; the position relating to multiple myeloma will need to be monitored carefully.


   Conflicts of interest
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
References
 
None declared


   Acknowledgements
 
We thank the original member companies of the BRMA for supporting this initiative and for abstracting data onto the study pro formas. We thank the ONS for supplying follow-up information and the BRMA for defraying the costs of this analysis.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
 References
 

  1. International Agency for Research on. Cancer. In: Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Humans. The Rubber Industry (1982) Vol. 28. Lyon: IARC.

  2. Kogevinas M, Sala M, Boffetta P, et al. Cancer risk in the rubber industry: a review of the recent epidemiological evidence. Occup Environ Med (1998) 55:1–12.[Abstract/Free Full Text]

  3. Straughan JK. Cancer risk in the rubber industry: a review of the recent epidemiological evidence. Occup Environ Med (1998) 55:646.[Free Full Text]

  4. Kogevinas M, Sala M, Boffetta P. Cancer risk in the rubber industry: a review of the recent epidemiological evidence. Occup Environ Med (1998) 55:646.[Free Full Text]

  5. Muir KR, Harriss C. Prostate Cancer and Occupation: A Literature Review. HSE Contract Research Report No. 191/1998 (1998) Sudbury: HSE Books.

  6. Sorahan T, Parkes HG, Veys CA, Waterhouse JAH, Straughan JK. Mortality in the British rubber industry, 1946 –85. Br J Ind Med (1989) 46:1–11.[Web of Science][Medline]

  7. Baxter PJ, Werner JB. Mortality in the British Rubber Industries, 1967–76 (1980) London: HMSO.

  8. Weiland SK, Straif K, Chambless L, et al. Workplace risk factors for cancer in the German rubber industry: part 1. Mortality from respiratory cancers. Occup Environ Med (1998) 55:317–324.[Abstract/Free Full Text]

  9. Straif K, Weiland SK, Werner B, Chambless L, Mundt KA, Keil U. Workplace risk factors for cancer in the German rubber industry: part 2. Mortality from non-respiratory cancers. Occup Environ Med (1998) 55:325–332.[Abstract/Free Full Text]

  10. Straif K, Weiland SK, Bungers M, et al. Exposure to high concentrations of nitrosamines and cancer mortality among a cohort of rubber workers. Occup Environ Med (2000) 57:180–187.[Abstract/Free Full Text]

  11. Straif K, Keil U, Taeger D, et al. Exposure to nitrosamines, carbon black, asbestos, and talc and mortality from stomach, lung, and laryngeal cancer in a cohort of rubber workers. Am J Epidemiol (2000) 152:297–306.[Abstract/Free Full Text]

  12. Wilczynska U, Szadkowska-Stanczyk I, Szeszenia-Dabrowska N, Sobala W, Strzelecka A. Cancer mortality in rubber tire workers in Poland. Int J Occup Med Environ Health (2001) 14:115–125.[Medline]

  13. Veys CA. Bladder tumours in rubber workers: a factory study 1946 –1995. Occup Med (2004) 54:322–329.[Abstract/Free Full Text]

  14. Veys CA. A study of mortality patterns at a tyre factory 1951 –1985: a reference statistic dilemma. Occup Med (2004) 54:330–335.[Abstract/Free Full Text]

  15. Straughan JK, Sorahan T. Cohort mortality and cancer incidence survey of recent entrants (1982 –91) to the United Kingdom rubber industry: preliminary findings. Occup Environ Med (2000) 57:574–576.[Abstract/Free Full Text]

  16. Sorahan T, Parkes HG, Veys CA. Waterhouse. Cancer mortality in the British rubber industry: 1946 –80. Br J Ind Med (1986) 43:363–373.[Web of Science][Medline]

  17. Parkes HG, Veys CA, Waterhouse JAH, Peters A. Cancer mortality in the British rubber industry. Br J Ind Med (1982) 39:209–220.[Web of Science][Medline]

  18. Dost AA, Redman D, Cox G. Exposure to rubber fume and rubber process dust in the general rubber goods, tyre and retread industries. Ann Occup Hyg (2000) 44:329–342.[Abstract/Free Full Text]


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