Skin cancer is the most common type of cancer (ACS 2004u). There are two forms of skin cancer: melanoma (ICD-9 172) and nonmelanoma (basal-cell and squamous-cell carcinomas) (ICD-9 173). The major risk factor for both types of skin cancer is exposure to the sun and other sources of UV radiation. Family history, fair skin, moles, male sex, the inherited disease xeroderma pigmentosum, and immune suppression also play a role in the development of melanoma skin cancers. Melanoma is a much less common form of skin cancer than basal-cell or squamous-cell carcinoma, but is much more serious, usually being fatal if not treated in its early stages (ACS 2004u).
In 2000, malignant melanoma accounted for 17.7 new cases per 100,000 people (22.5 among men and 14.4 among women) and 2.7 deaths per 100,000 (3.8 among men and 1.8 among women) in the United States (Ries et al. 2004).
Most of the studies identified by the committee as meeting its criteria for assessing a potential association between exposure to fuels or their combustion products and skin cancer focused on melanoma. Mortality studies are likely to focus on melanoma, because it is unusual to die of other forms of skin cancer. Several studies of ocular melanoma or uveal melanoma (ICD-8 191) were identified; these are considered separately from cutaneous melanoma because they are classified as malignant neoplasms of nervous tissue. Mortality and morbidity studies of cutaneous melanoma are presented below; information gathered on malignant nonmelanoma skin cancer is summarized in the next section.
Table 4.21 presents the most relevant findings considered by the committee in drawing its conclusion on the possibility of an association between exposure to fuels and melanoma skin cancer.
In the large Amoco cohort of oil refinery workers, Nelson et al. (1987) found the risk of skin-cancer death among white men increased (SMR 2.01, 95% CI 1.00–3.60), even though the usual “healthy-worker effect” of reduced overall mortality and cancer mortality was seen. The study combined both melanoma and nonmelanoma skin cancer in its definition of skin cancer; however, because death was the end point, virtually all the skin-cancer cases were probably melanoma. When latent period was considered, the mortality was greatest among those with less than 15 years since first exposure (SMR 5.24, p<0.05). The work histories of the people in the cohort were reviewed by industrial hygienists and classified for specific exposures (Nelson et al. 1985). There were 11 skin cancers, and the excess appeared to be concentrated among the maintenance workers (SMR 3.78, p<0.05). Routine exposure to refinery processes was also associated with skin-cancer mortality (SMR 2.68, p<0.05). The failure to adjust for possible confounders (particularly sun exposure) reduces confidence in the finding.
Jarvholm et al. (1997) investigated the incidence of melanoma and nonmelanoma skin cancer separately in a cohort of Swedish refinery workers. A minor increase in the risk of melanoma (SIR 1.1, 90% CI 0.49–2.0) was based on seven exposed cases, who had all received their diagnoses within 20 years of their first exposure.