There are three histological types of non-melanocytic skin cancers (NMSC) (ICD-9: 173; ICD-10: C44): basal cell carcinoma, squamous cell carcinoma and rare soft tissue sarcomas involving the skin, subcutaneous tissue, sweat glands, sebaceous glands and hair follicles.

Basal cell carcinoma is the most common NMSC in white populations, representing 75 to 80% of them. It develops usually on the face, grows slowly and has little tendency to metastasize.

Squamous cell cancers account for 20 to 25% of reported NMSCs. They can occur on any part of the body, but especially on the hands and legs and can metastasize. In darkly pigmented populations squamous cell cancers are the most common NMSC.

Multiple primary NMSCs are common. The bulk of the NMSCs occur on the head and neck, in contrast with most of the melanomas which occur on the trunk and limbs. The localization of NMSCs reflects clothing patterns.

NMSCs are treated by various methods of excision, radiation and topical chemotherapy. They respond well to treatment and over 95% are cured by excision (IARC 1990).

The incidence of NMSCs is hard to estimate because of gross underreporting and since many cancer registries do not record these tumours. The number of new cases in the US was estimated at 900,000 to 1,200,000 in 1994, a frequency comparable to the total number of all non-cutaneous cancers (Miller & Weinstock 1994). The reported incidences vary widely and are increasing in a number of populations, e.g., in Switzerland and the US. The highest annual rates have been reported for Tasmania (167/100,000 in men and 89/100,000 in women) and the lowest for Asia and Africa (overall 1/100,000 in men and 5/100,000 in women). NMSC is the most common cancer in Caucasians. NMSC is about ten times as common in White as in non-White populations. The lethality is very low (Higginson et al. 1992).

Susceptibility to skin cancer is inversely related to the degree of melanin pigmentation, which is thought to protect by buffering against the carcinogenic action of solar ultraviolet (UV) radiation. Non-melanoma risk in white-skinned populations increases with the proximity to the equator.

In 1992, the International Agency for Research on Cancer (IARC 1992b) evaluated the carcinogenicity of solar radiation and concluded that there is sufficient evidence in humans for the carcinogenicity of solar radiation and that solar radiation causes cutaneous malignant melanoma and NMSC.

Reduction of exposure to sunlight would probably reduce the incidence of NMSCs. In Whites, 90 to 95% of NMSCs are attributable to solar radiation (IARC 1990).

NMSCs may develop in areas of chronic inflammation, irritation and scars from burns. Traumas and chronic ulcers of the skin are important risk factors for squamous cell skin cancers, particularly in Africa.

Radiation therapy, chemotherapy with nitrogen mustard, immunosuppressive therapy, psoralen treatment combined with UV-A radiation and coal tar preparations applied on skin lesions have been associated with an increased risk of NMSC. Environmental exposure to arsenic trivalent and arsenical compounds have been confirmed to be associated with skin cancer excess in humans (IARC 1987). Arsenicism can give rise to palmar or plantar arsenical keratoses, epidermoid carcinoma and superficial basal cell carcinoma.

Hereditary conditions such as lack of enzymes required to repair the DNA damaged by UV radiation may increase the risk of NMSC. Xeroderma pigmentosum represents such a hereditary condition.

A historical example of an occupational skin cancer is scrotal cancer that Sir Percival Pott described in chimney sweeps in 1775. The cause of these cancers was soot. In the early 1900s, scrotal cancers were observed in mulespinners in cotton textile factories where they were exposed to shale oil, which was used as a lubricant for cotton spindles. The scrotal cancers in both chimney sweeps and mulespinners were later associated with polycyclic aromatic hydrocarbons (PAHs), many of which are animal carcinogens, particularly some 3-, 4- and 5-ring PAHs such as benz(a)pyrene and dibenz(a,h)anthracene (IARC 1983, 1984a, 1984b, 1985a). In addition to mixtures that readily contain carcinogenic PAHs, carcinogenic compounds may be formed by cracking when organic compounds are heated.

Further occupations with which PAH-related excesses of NMSC have been associated include: aluminium reduction workers, coal gasification workers, coke oven workers, glass blowers, locomotive engineers, road pavers and highway maintenance workers, shale oil workers, tool fitters and tool setters (see table 1). Coal tars, coal-based pitches, other coal-derived products, anthracene oil, creosote oil, cutting oils and lubricating oils are some of the materials and mixtures that contain carcinogenic PAHs.

Table 1. Occupations at risk

Additional job titles that have been associated with increased NMSC risk include jute processors, outdoor workers, pharmacy technicians, sawmill workers, shale oil workers, sheep-dip workers, fishermen, tool setters, vineyard workers and watermen. The excess for watermen (who are primarily involved in traditional fishing tasks) was noticed in Maryland, USA and was confined to squamous cell cancers. Solar radiation probably explains fishermen’s, outdoor workers’, vineyard workers’ and watermen’s excess risks. Fishermen also may be exposed to oils and tar and inorganic arsenic from the consumed fish, which may contribute to the observed excess, which was threefold in a Swedish study, as compared with the county-specific rates (Hagmar et al. 1992). The excess in sheep dip workers may be explained by arsenical compounds, which induce skin cancers through ingestion rather than through skin contact. While farmers have slightly increased risk of melanoma, they do not appear to have increased risk of NMSC, based on epidemiological observations in Denmark, Sweden and the USA (Blair et al. 1992).

Ionizing radiation has caused skin cancer in early radiologists and workers who handled radium. In both situations, the exposures were long-lasting and massive. Occupational accidents involving skin lesions or long-term cutaneous irritation may increase the risk on NMSC.

Prevention (of Non-Melanocytic OccupationalSkin Cancer)

The use of appropriate clothing and a sunscreen having a protective UV-B factor of 15 or greater will help protect outdoor workers exposed to ultraviolet radiation. Further, the replacement of carcinogenic materials (such as feed stocks) by non-carcinogenic alternatives is another obvious protective measure which may, however, not always be possible. The degree of exposure to carcinogenic materials can be reduced by the use of protective shields on equipment, protective clothing and hygienic measures.

Of overriding importance is the education of the workforce about the nature of the hazard and the reasons for and value of the protective measures.

Finally, skin cancers usually take many years to develop and many of them pass through several premalignant stages before achieving their full malignant potential such as arsenic keratoses and actinic keratoses. These early stages are readily detectable by visual inspection. For this reason, skin cancers offer the real possibility that regular screening could reduce mortality among those known to have been exposed to any skin carcinogen.

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