CHAPTER 11

CORRELATIONS WITH SOCIOECONOMIC STATUS AND OCCUPATIONAL FACTORS

INTRODUCTION

In this chapter, three potential risk factors for cutaneous malignant melanoma (CMM) are discussed. First, the epidemiologic studies which have examined trends in CMM according to socioeconomic status and general occupational classifications are reviewed. Second, studies on the occurrence of CMM among workers exposed to chemicals or radiation are described. Third, the epidemiologic data on the development of CMM among indoor workers exposed to fluorescent lighting are reviewed. Although these areas are addressed separately, they all focus on the potential links between CMM and occupation.

MELANOMA TRENDS ACCORDING TO SOCIOECONOMIC STATUS

Potential relationships between socioeconomic status and CMM incidence and mortality have been analyzed in several epidemiologic studies. Variables used to reflect socioeconomic status have included occupational groups (e.g., professional vs. laborer), types of work (e.g., indoor office vs. outdoor), and general indicators such as education and income. The results of these studies have not produced a clear understanding of the relationship of CMM to socioeconomic status. Several epidemiologic studies have indicated that CMM incidence and mortality are positively related to socioeconomic status (Holman et al. 1980; Lee and Strickland 1980; MacKie and Aitchison 1982; Cooke et al. 1984; Aquavella et al. 1983; Teppo et al. 1980). While some studies have shown that outdoor workers do not have an elevated risk of melanoma compared to office workers (Lee and Strickland 1980; Cooke et al. 1984), other studies have indicated that outdoor workers have slightly elevated CMM risks for normally uncovered parts of the body such as the face and neck (Beral and Robinson 1981; Vagero et al. 1986). Professional and administrative type office workers, but not other indoor workers, have been shown to be at elevated CMM risk compared to outdoor workers (Lee and Strickland 1980; Holman et al. 1980) and to have an elevated risk of CMM on normally covered parts of the body (Beral and Robinson 1981; Vagero et al. 1986).

One epidemiologic study which specifically examined trends in melanoma by socioeconomic status was conducted by Lee and Strickland (1980). Data on CMM incidence by occupation were obtained for 1968 to 1970 from the Supplement on the Registrar General's Statistical Review of England and Wales. Mortality data for England and Wales were obtained from the Occupational Mortality Decennial Supplements for the periods 1949-1953, 1959-1963, and 1970-1972. Standardized mortality ratios (SMRs) were based on census population statistics corresponding to 1951, 1961, and 1971. Because there were no population data for the British cancer registration data, the incidence data were analyzed by proportional ratios which compared the proportion of incident melanomas to all cancers for each occupational group. The authors noted that the ratios were susceptible to distortion by large risk differences between occupational groups (e.g., lung cancer), but stressed that they may be useful in conjunction with other information. Social class categories consisted of I (professional), II (intermediate), III (skilled workers including manual, IIIM, and non-manual, IIIN), IV (semi-skilled), and V (unskilled).

Lee and Strickland (1980) observed a general trend of increasing SMRs for CMM with increasing social class for males from 1949 to 1972 (Table 11-1). A comparison of SMRs according to finer occupational groupings (as outlined in Table 11-2) showed that outdoor workers (e.g., farmers and construction workers) did not have higher SMRs than indoor workers such as warehousemen, shopkeepers, or engineers, and had lower SMRs than professional, technical, administrative, and managerial workers. A similar comparison using the CMM incidence data also indicated higher standardized proportional registration ratios among professional and administrative workers than among construction workers, engineers, and warehousemen. Lee and Strickland (1980) concluded that their results suggested a relationship between CMM incidence and some feature of life associated with education or economic status. Lee (1982) also noted that these results showed the lack of a marked effect of outdoor occupation on CMM mortality.

A study conducted by Holman et al. (1980) also identified differences in melanoma incidence rates according to social class and occupation. Holman et al. (1980) analyzed melanoma incidence data for 1975 and 1976 obtained from hospital and pathology records in Western Australia. Information on the 120 pre-invasive melanoma (PIM) and 422 invasive malignant melanoma (IMM) cases included occupation and location of usual residence. Social classes were assigned from 1 to 4 based on socioeconomic data for each residential area. As shown in Table 11-3, for IMM cases, the highest incidence rates among males and females occurred in social class 1. Among females, the incidence rates declined with lower social class; the relationship was more complex among males. For PIM, a pattern was not evident. Controlling for country of birth and proximity to sea did not alter the apparent relationship between social class and IMM incidence. Table 11-4 indicates that the highest incidence rates occurred among professional, clerical, sales, administrative, and managerial workers, whereas the lowest rates occurred among laborers, tradesmen, farmers, and fishermen. Holman et al. (1980) observed that although these results were consistent with an association between melanoma incidence and social class, they were not what would have been expected if total exposure to the sun were a predominant causal variable. They hypothesized that the results could be explained if intermittent (e.g., recreational) sun exposure were more likely to induce malignant melanoma than continuous exposure. In addition, differences in host factors and ethnic background by social class could also partially explain these observations.

MacKie and Aitchison (1982) conducted a case-control study on 113 CMM patients presenting with primary CMM in West Scotland from 1978 to 1980 and 113 age- and sex-matched controls. Matched case-control comparisons were analyzed using conditional multiple logistic regression. Information on each case included positive history of recreational or occupational sun exposure (classified as 16 or more hours outdoors per week), social class (V, unskilled, to I, professional), and history of severe sunburn. When the data were analyzed for males and females combined, melanoma patients were of higher social class and had lower recreational sun exposures than controls (p<0.05). Among males only, socioeconomic status and history of severe sunburn were significantly higher for cases compared to controls (p<0.05). Occupational exposure was significantly less in males cases than controls (p<0.05). Among females, the only significant difference was the higher incidence of severe sunburn among the CMM patient group. MacKie and Aitchison (1982) concluded that melanoma appeared to be more common among higher socioeconomic classes and for male professional or administrative workers. The authors questioned the accuracy of the socioeconomic status data on females since these were classified as those of their husband. They also claimed that their results confirmed the hypothesis that isolated episodes of intense burning sun exposure may be an important factor in melanoma.

In a more recent study, Cooke et al. (1984) examined CMM incidence and mortality data for 1972-1976 and 1973-1976, respectively, for New Zealand non-Maori males aged 25-64. The 501 incident cases and 142 melanoma mortality cases were classified according to occupation and then reclassified by socioeconomic status (based on income and education) and average outdoor occupational exposure (10 or more, 2-10, or 2 or less hours outdoors per week). Standardized incidence and mortality ratios were calculated for four 10-year age groups by indirect standardization based on 1971 and 1976 census data. When analyzed by major occupational group (Table 11-5), the observed number of incident melanoma cases significantly exceeded the expected number (p<0.001) for professional/technical and administrative/managerial workers. The observed number of incident melanoma cases was significantly lower than expected (p<0.001) for production, transportation, and labor occupational categories. Smaller differences were noted when similar comparisons were made for the mortality data.

Table 11-6 displays the Cooke et al. (1984) age-standardized incidence data reclassified according to anatomical site, socioeconomic status, and outdoor vs. indoor exposure. Trends in the data according to socioeconomic status were apparent for melanomas of each site (e.g., the head and neck, trunk, and upper and lower limbs) among indoor workers. Among outdoor workers, socioeconomic trends were observed only for melanomas of the trunk. This analysis was, however, limited by the small number of registrations in some groups and the fact that 37 of 501 incident cases did not have site information (these cases were spread across all age groups). The authors concluded that the elevated melanoma incidence rates among professional, technical, administrative, and managerial workers appeared to be due to differences in socioeconomic status. They observed that there was no evidence of differences in risk between indoor and outdoor workers of similar socioeconomic classes. Similar results were observed for the mortality data when analyzed according to age, socioeconomic status, and outdoor exposure.

Cooke et al. (1984) concluded that their results did not support the hypothesis that recreational sunbathing of inadequately tanned skin is important in the etiology of melanoma. The similarity between outdoor and indoor workers implied that solar exposure was unlikely to have been important. The authors noted, however, that different patterns of recreational sun exposure (e.g., sunny winter holidays or use of sun lotions) may have sufficiently varied within social classes to have overcome the tendency of greater exposure of outdoor workers.

Several case-control studies have also examined trends in melanoma with respect to outdoor occupational exposure patterns. A Norwegian case-control study by Klepp and Magnus (1979) found outdoor work (3-4 hours per day in fresh air at work) to be more prevalent among their 35 male melanoma patients (40 percent) than among their 92 other non-skin cancer, male, non-matched controls from the same hospital (32 percent), but this difference was not statistically significant. Results from another case-control study, conducted by MacKie and Aitchison (1982) in West Scotland, are the reverse of the findings by Klepp and Magnus in Norway (1979). MacKie and Aitchison (1982) showed significantly lower levels of occupational sun exposure (p<0.05) among 52 male melanoma patients compared with 52 age-matched male controls. Twenty-three percent of the male cases had positive occupational exposure (16 or more hours outdoors each week) as compared with 48 percent of the controls.

In a much larger case-control study conducted in Western Canada (595 age-, sex-, and residence-matched pairs), Elwood et al. (1985) assessed sun exposure using a lifetime occupational history with information on each job, industry, and usual numbers of outdoor hours per week on the job during the summer and winter seasons. Results of a multiple logistic regression analysis showed a significantly increased relative risk of 1.6 for those with "mild" occupational sun exposure during summer (approximately 1-8 hours/week) compared to those with no occupational sun exposure. After adjustment for host factors (hair color, skin color, history of freckles) and ethnic origin, the relative risk increased slightly to 1.8 (95% C.I. 1.2-2.5) at the same mild exposure level. No increased risk was seen, however, at higher occupational sun exposure levels (8-16 hours/week, 16-32 hours/week, or 32+ hours/week).

The effect of clothing habits during outdoor work on the risk of melanoma was examined by Holman et al. (1986) in a case-control study of CMM cases in Western Australia (507 age-, sex-, and residence-matched pairs). This is one of the few studies which investigated histogenic types of CMM and sunlight exposure patterns. For all melanomas combined and all histogenic types except SSM, the risks were higher if the primary melanoma site was sometimes exposed rather than usually exposed or usually covered while working outdoors. SSM, in contrast, showed a significant increasing linear trend (p=0.008) for site exposure as follows: OR=1.0 for "usually covered," OR=2.16 (95% C.I. 1.14-4.10) for "sometimes exposed," and OR=2.43 (95% C.I. 1.18-4.97) for "usually exposed." This result, which contradicts the hypothesis that intermittent exposure is important in the development of SSM, was not specifically discussed by the authors.

In a cohort study using college health records from 50,000 male alumni of Harvard University and the University of Pennsylvania to identify predictive risk factors for fatal skin, blood, and lymphatic cancers, Paffenbarger et al. (1978) found an increased relative risk of melanoma (RR=3.9, p=0.01) for outdoor work prior to college. This was based on 45 deaths from malignant melanoma during the 35-year observation period (1.71 million person-years of observation) compared with 180 surviving controls (4 controls per case were chosen from classmates born in the same year and known to survive the decedent). There was no information on outdoor work after university admittance, but previous outdoor work was the only significant risk factor identified for melanoma in this study.

A study of CMM incidence data for England and Wales by Beral and Robinson (1981) revealed site-specific trends according to occupation. They examined melanoma and basal and squamous cell cancer incidence data from 1970 to 1975 for England and Wales obtained from the Office of Population Censuses and Surveys. Information for each case included occupation and, for each melanoma case, anatomical location. The anatomical location data were grouped into either exposed (head, face, and neck) or unexposed site categories. Occupational groups were classified as indoor office workers, other indoor workers, or outdoor workers. Age-specific standardized cancer registration ratios were calculated by indirect standardization and based on 1971 census

Table 11-7 shows the age-standardized registration ratios for melanomas of exposed and unexposed sites, and other skin cancers, by place of work for males aged 15-64 years. These results indicate that outdoor work was associated with a 10 percent excess of basal and squamous cell carcinomas, a 9 percent nonsignificant excess of melanomas of the head, face and neck, and a 22 percent deficit of melanomas of unexposed sites. In contrast, office work was associated with a 31 percent excess of melanomas of unexposed sites. These differences persisted when the data were analyzed for social class III (skilled workers) only, as shown in Table 11-8. There was, however, one main difference--office work was also significantly associated with an excess of squamous cell and basal cell carcinomas (p<0.05).

Beral and Robinson (1981) concluded that the similarity of melanomas of "exposed" sites and squamous and basal cell carcinomas by occupational group suggested that prolonged sun exposure may be important in the etiology of melanomas of regularly exposed parts of the body. Furthermore, the low incidence of melanomas of unexposed sites in outdoor workers indicated that occupational exposure was not associated with increased melanoma incidence on normally covered parts of the body. The authors noted that the reasons for differences between office workers and other indoor workers (who had lower melanoma and other skin cancer incidence rates) were not clear. They observed, however, that whatever the cause (e.g., a greater tendency to expose normally covered parts of the body to sunlight), it was unlikely that prolonged sun exposure was an important etiological factor in office workers.

A recent study by Vagero et al. (1986) confirms some of the findings of Beral and Robinson (1981). Vagero et al. (1986) examined incidence data on 4,706 CMM cases and 4,244 basal and squamous cell carcinoma cases for 1961 to 1979 from the Swedish Cancer Environment Registry. The data were classified by occupation (office, other indoor, and outdoor workers), and anatomical location for CMM cases (covered and uncovered parts of the body). Standardized Morbidity Ratios (SMBRs) were calculated based on 1960 population census data and adjusted for age, sex, residence, and social class.

A comparison of the calculated SMBRs for males and females combined is shown in Table 11-9. The results were consistent with a slightly higher risk of melanoma of the face and neck for outdoor workers. For office workers, however, the observed number of melanomas was lower than expected for normally uncovered parts of the body and higher than expected for normally covered parts. Vagero et al. (1986) concluded that the elevated risk of melanoma of covered parts of the body among office workers was not entirely due to differences in social class. They estimated that indoor office workers, as compared to other indoor workers, may have a 10 percent greater CMM incidence after taking into account differences in age, residence, and social class distribution. The authors hypothesized that the observed differences in CMM incidence did not merely reflect risk differences between social classes such as those assumed to be caused by different patterns of sun exposure. Such differences would not explain the contrasts between office and other indoor workers within the same social class which have been observed in this and other studies (Lee and Strickland 1980; Beral and Robinson 1981). However, the authors could not rule out the possibility that within each social class, patterns of sunlight exposure and sunburn experience were different among office, other indoor, and outdoor workers.

MELANOMA IN WORKERS EXPOSED TO CHEMICALS OR RADIATION

There have been a number of studies in which an increased incidence of cutaneous melanoma has been reported in cohorts occupationally exposed to chemicals and/or radiation. Rushton and Alderson (1981) evaluated mortality records for workers in eight oil refineries in Britain. To be included in the study, workers had to have worked for at least 1 year between January 1, 1950 and December 31, 1975. The study population consisted of 34,701 white males, with 575,982 person-years of observation and a mean follow up of 16.6 years. Comparison populations were males in England and Wales for the English and Welsh refineries, and in Scotland for the Scottish refineries. Data were analyzed across all refineries or by individual refineries but there was very little ancillary information on the differences between refineries with regard to location, size of work force, type of product produced, or length of service.

Two refineries showed a significant excess of observed melanoma deaths vs. expected deaths: p=0.0037 for refinery B and p=0.0003 for refinery H. At refinery B, four out of five individuals who died from melanoma were "operators," whereas at refinery H, the six deaths included an operator, two boilermakers, a pipefitter, a laborer, and a clerk. There was no definition of the exposure pattern normally encountered by these various positions, nor was it possible to determine what either refinery produced, and thus to what these individuals may have been exposed.

Hoar and Pell (1981), in a retrospective cohort study of chemists working for E.I. DuPont Company, evaluated records from 3,713 white males and 75 white females who were employed in 1959 as chemists as well as 19,262 white males and 673 white females who were "non-chemists." The authors indicated that the job title "chemist" at DuPont was difficult to define, that most chemists were exposed to a number of chemicals that changed in quantity and quality, and that different chemists rarely had the same exposures. Thus it was not possible to even estimate the kinds of chemicals to which "chemists" were exposed. The title "non-chemist" was applied only to people who had never been chemists. In addition, their exposures were also not stated. Death certificates were obtained on 105 (93 percent) of the male and 6 (100 percent) of the female deceased chemists, and on 1,863 (92 percent) of the male and 15 (79 percent) of the female deceased non-chemists.

When compared to the non-chemist cohort, melanoma incidence in the male chemists was not significantly different. However, when compared to the Third National Cancer Survey, the incidence of melanoma among male chemists was more than expected (O/E=8/3.3; standardized incidence ratio of 239, 95% C.I.=111-454). A subsequent comparison of the non-chemist cohort to the Third National Cancer Survey revealed that this group too showed a higher than expected incidence (O/E=38/17.1; standardized incidence ratio of 223, C.I. not provided).

In discussing the above finding, the authors indicated that a similar observation was made for all DuPont employees in the period 1956-1974 and that one possible explanation may have been occupational exposure to chemicals suspected of being skin carcinogens. Another possible explanation suggested by the authors was exposure to solar radiation. The majority of DuPont plants are located in the Southeastern United States, where solar exposure is greatest. Sixty-five percent of the DuPont salaried employees resided in the 15 southern states which account for 37 percent of U.S. melanoma mortality.

Holmbert et al. (1983) studied a cohort of 13,114 persons who had worked at two plants in the Swedish rubber industry for at least 12 months between January 1, 1951, and December 31, 1975. Workers were placed into one of three exposure categories. Category 1, work in the weighing and mixing department, consisted of 739 individuals. Category 2, other production work (e.g., calendaring, vulcanization, pressing, tire building, inspection, service work, floor cleaning, storage work), consisted of 9,883 individuals. Category 3, white collar work (office personnel, department heads), consisted of 2,492 individuals. An increased occurrence of malignant melanomas was found in Category 2, resulting in a risk ratio for this group of 2.50.

There is one brief report in the literature linking exposure to a specific class of chemicals with an increased incidence of melanoma. NIOSH (1976) and Bahn et al. (1976) reported increased mortality from melanoma in a cohort of workers exposed to Aroclor 1254 (Monsanto's tradename for PCBs) during a 9-year period in the late 1950's at a petrochemical plant in the northeast United States. The study evaluated information from two small cohorts: one of 51 workers at a research and development facility exposed from 1949 to 1957, and one of 41 workers in a refinery exposed from 1953 to 1958. Two melanomas occurred in the first cohort (vs. 0.04 expected, p<0.001). In the second cohort of 51 workers, excess melanomas were observed; however, no detailed information was provided on exposure or method of analysis. There was no attempt to quantify or even describe exposures in this workplace and it is possible that these workers were exposed to chemicals other than PCBs.

In the period of 1972 to 1977, 19 cases of melanoma were reported among approximately 5,100 employees of the Lawrence Livermore National Laboratory (LLNL) (Austin et al. 1981). This was approximately three times the rate expected in a comparable age/race/sex-adjusted geographical segment of the population from the San Francisco Bay area. To investigate this finding, each case was matched with four controls drawn from the laboratory population and analyzed to examine the relationship of risk to occupational variables such as length of employment, cumulative radiation exposure, and job classification ("scientist" vs. "non-scientist"). Cases and controls were matched on the basis of 5-year age group, race, sex, and census tract. No relationship was evident between melanoma and any of these parameters; however, "chemists" had a relative risk of 6.97 (p=0.011).

In an attempt to control for socioeconomic differences between the study group and reference groups, cases and controls were matched by census tract of residence in the incidence analysis. It was not possible to evaluate the efficacy of this technique, but since the difference in melanoma incidence between the highest and lowest quartiles of SES for all census tracts in the San Francisco SMSA was only twofold, it seems unlikely that SES differences accounted for the finding at LLNL. Beyond the conclusion that this was a real increase in the incidence of melanoma that could not be accounted for by other factors such as socioeconomic status, the authors were unable to identify a work-related factor (other than job title) which showed an association with melanoma incidence in this population.

As a result of the LLNL report, Acquavella et al. (1983) conducted a case-control study of melanoma at the Los Alamos National Laboratory (LANL). Twenty cases were identified and, for each case, four controls were selected and matched on the basis of sex, ethnicity, date of birth, and date of first employment. Controls were selected from employees hired immediately before and after each case. Most controls were selected from a pool of 100 employees but occasionally this was expanded to as large as 500 in order to obtain adequate matches. The data obtained for cases and controls included a number of occupational variables such as length of employment, cumulative external radiation exposure 2 years prior to case's occurrence of melanoma, job title, and educational status. The authors concluded that there was no indication of an association between melanoma occurrence and any particular form of radiation. With regard to educational attainment, however, individuals with a college or graduate level degree had elevated risks of developing melanoma. College graduates had a standardized rate ratio (SRR) of 2.11 and those with a graduate degree had an SRR of 3.17.

MELANOMA AND EXPOSURE TO FLUORESCENT LIGHTING

Several studies have examined the potential link between exposure to fluorescent lighting and CMM. Interest in this area developed in response to information indicating apparent differences in melanoma incidence between outdoor workers and indoor office workers who are regularly exposed to fluorescent light. Emissions from fluorescent lights often extend into the UV range, although the emitted wavelength distribution varies with the type of lamp, glass envelope, and other covers.

Beral et al. (1982) analyzed data on 274 female cases of CMM 18-54 years of age and 549 age- and residence-matched female controls from a study originally designed to investigate the association between melanoma and oral contraceptive use in New South Wales, Australia. They found exposure to fluorescent light at work to be associated with a 2.1 relative risk of melanoma (95% C.I. 1.32-3.32) as compared to no exposure at work. This risk increased with increasing duration of exposure (p<0.001 for trend) and was higher for women who had worked mainly in offices (RR=2.6) than for those who had worked mainly indoors but not in offices (RR=1.8). The increase in risk associated with fluorescent light exposure at work was further examined to determine whether other factors might be indirectly affecting the risk. Neither long-term nor intense short-term recreational exposure to sunlight showed a consistent relationship to increased melanoma risk, nor did stratification by the following factors diminish the overall association: amount of time spent outdoors, main outdoor activity and amount of clothing worn in childhood and at ages 20 and 30, sunburn history on various parts of the body, place of birth, hair color, skin color, use of oral contraceptives, and frequency of naevi on the body. Some of these factors, however, seemed to modify the risk of melanoma associated with exposure to fluorescent light slightly, e.g., the relative risks tended to be lower for women who had been most heavily sun-exposed, as estimated by amount of time spent outdoors in childhood and main outdoor activity at age 20 and higher for women who reported having more than an average number of naevi. In contrast with these results, there was no increase in melanoma risk for fluorescent lights in the home (RR=0.9, 95% C.I. 0.6-1.6) even when analysis was restricted to women who had never been exposed to fluorescent lights at work and who had never worked outdoors.

A small series of 27 male melanoma cases 18-56 years of age and 35 male controls of similar ages was available from the same melanoma clinic (Beral et al. 1982) and showed a similar significant increase in melanoma risk with exposure to fluorescent light among those who always worked indoors. The relative risk of CMM for males with 10 or more years of fluorescent light exposure (RR=4.4, 95% C.I. 1.1-17.5) was higher than the relative risks for women with more than 10 years of exposure, although confidence limits overlapped (10-19 years, RR=2.5, 95% C.I. 1.5-4.2; 20 or more years, RR=2.6, 95% C.I. 1.2-5.9). The males also showed slightly higher melanoma risk for ever having worked outdoors compared to those who had always worked indoors (RR=2.2, 95% C.I. 0.6-8.0). Although results are based on small numbers of male CMM cases and controls, the findings are in agreement with those from the larger study of females.

Dubin et al. (1986) also examined the association of CMM to fluorescent light exposure in an interview study of 1,103 CMM cases and 585 controls randomly chosen among new patients, ages 20 and older, at the New York University Skin and Cancer Unit general skin clinic. A preliminary analysis of a subset of these data (Pasternack et al. 1983) yielded a significant positive association between CMM and fluorescent light exposure. A reliability study was later conducted to confirm the interview assessment of fluorescent light exposure by means of a mailed questionnaire. The reliability study data did not support the interview data that formed the basis of their preliminary report (Pasternack et al. 1983) of a positive association of CMM to fluorescent light exposure. Dubin et al. (1986) believe that interview bias may have affected the fluorescent light data, leading to overestimates of exposure only among cases but not controls For this reason, no conclusions regarding the association of CMM to fluorescent light exposure can be drawn from this study.

Elwood et al. (1986) conducted a matched case-control study of 83 CMM patients and 83 age-, sex-, and residence-matched controls which evaluated exposure to both diffused and undiffused fluorescent lighting. No significant trends in relative risk were associated with level of exposure to fluorescent lighting through occupational or home exposure. The relative risk for individuals in the highest total occupational fluorescent light exposure category (50,000+ hours) compared to those with no occupational exposure was 1.4 (95% C.I.=0.4-5.1). Corresponding relative risks for those exposed to the highest categories of diffused (25,001-50,000 hours) and undiffused (50,000+) fluorescent lighting were 1.5 (95% C.I.=0.5-4.4 and 4.0 (95% C.I.=0.8-19.2), respectively. Associations of CMM with fluorescent lighting based on a subsequent postal questionnaire were weaker than those based on the personal interviews cited above. This also occurred in the study of Dubin et al. (1986), and may involve either recall bias in personal interviews or the fact that mailed questionnaires are less reliable than personal interviews (Elwood et al. 1986).

Rigel et al. (1983) found no increased risk of melanoma associated with fluorescent-light exposure in a preliminary analysis of 114 melanoma patients and 228 matched (5-year age groups) controls from the New York University Medical Center. There was no significant difference in the proportion of indoor office workers between the cases (57 percent) and the controls (60 percent), nor was there a difference in average daily exposure to fluorescent lights (4.9 hours for cases and 5.4 hours for controls). For indoor office work, the average daily amount of fluorescent light exposure was 5.93 hours for cases vs. 5.99 hours for controls. The authors found increased risks for several risk factors, e.g., recreation activities (RR=2.4, p=0.01 for outdoor vs. indoor) and sun exposure 2 hours/day (11-20 years ago RR=2.5, p=0.0005 and 6-10 years ago RR=1.6, p=0.05). They postulate that the increased melanoma risk for indoor workers may be explained by their recreational habits and not by fluorescent-light exposure.

FINDINGS

A number of findings are noteworthy regarding patterns of CMM with respect to socioeconomic status and other occupational factors:

11.1 CMM incidence and mortality show a positive association with increasing socioeconomic status. Furthermore, total CMM incidence has been observed to be higher among "professional" and "administrative" indoor office workers, but not other indoor workers, compared to outdoor workers. Evidence indicating that outdoor workers do not have an elevated risk of melanoma compared to office workers may be confounded by differences in socioeconomic status, host factors, ethnic background, melanoma site, and histologic type.

11.2 For usually uncovered parts of the body (e.g., the face), the incidence and risk of CMM is higher among outdoor workers than among indoor office workers. For usually covered parts of the body, the incidence of CMM among indoor office workers is higher than for outdoor workers.

11.3 The incidence and risk of CMM among indoor office workers is higher for sites that are usually covered (e.g., the trunk) than for sites that are usually exposed (e.g., the face). Among outdoor workers, CMM risks are higher for usually exposed sites than for usually covered sites.

11.4 A number of studies investigating the melanoma risk of workers in refineries, or chemical or pharmaceutical plants, have failed to find a significant association between melanoma and potential exposure to chemicals, although in at least one study an increased risk of melanoma was found for male DuPont workers (both chemists and non-chemists) when compared to males from the Third National Cancer Survey. In one study from Lawrence Livermore National Laboratories, an increased risk of melanoma was observed in individuals with the title "chemist"; however, no other work-related factor demonstrated an association.

11.5 It has been suggested that the risk of developing CMM may be elevated among individuals exposed to fluorescent lighting at work. However, several studies have failed to find a significant and consistent association between CMM and exposure to fluorescent lighting at work. In addition, although two of these studies initially found an association based on personal interview data, an attempt by one study to validate its findings using a self-administered postal survey was not successful.

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