The effect of other types of radiation, such as cosmic radiation, is also controversial. Pilots and flight attendants have a reported incidence of SCC that ranges between 2.1 and 9.9 times what would be expected; however, the overall cancer incidence is not consistently elevated. Some attribute the high rate of nonmelanoma skin cancers in airline flight personnel to cosmic radiation, while others suspect lifestyle factors.[15,16,17,18,19,20]
Other environmental factors
The influence of arsenic on the risk of nonmelanoma skin cancer is discussed in detail in the Other environmental factors section in the Basal Cell Carcinoma section of this summary. Like BCCs, SCCs appear to be associated with exposure to arsenic in drinking water and combustion products.[21,22] However, this association may hold true only for the highest levels of arsenic exposure. Individuals who had toenail concentrations of arsenic above the 97th percentile were found to have an approximately twofold increase in SCC risk. For arsenic, the latency period can be lengthy; invasive SCC has been found to develop at an average of 20 years after exposure.
Current or previous cigarette smoking has been associated with a 1.5-fold to 2-fold increase in SCC risk,[25,26,27] although one large study showed no change in risk. Available evidence suggests that the effect of smoking on cancer risk seems to be greater for SCC than for BCC.
Additional reports have suggested weak associations between SCC and exposure to insecticides, herbicides, or fungicides.
Characteristics of the skin
Like melanoma and BCC, SCC occurs more frequently in individuals with lighter skin than in those with darker skin.[3,30] However, SCC can also occur in individuals with darker skin. An Asian registry based in Singapore reported an increase in skin cancer in that geographic area, with an incidence rate of 8.9 per 100,000 person-years. Incidence of SCC, however, was shown to be on the decline. SCC is the most common form of skin cancer in black individuals in the United States, and the mortality rate for this disease is relatively high in this population. Epidemiologic characteristics of, and prevention strategies for, SCC in those individuals with darker skin remain areas of investigation.
Freckling of the skin and reaction of the skin to sun exposure have been identified as other risk factors for SCC. Individuals with heavy freckling on the forearm were found to have a 14-fold increase in SCC risk if freckling was present in adulthood, and an almost threefold risk if freckling was present in childhood.[32,33] The degree of SCC risk corresponded to the amount of freckling. In this study, the inability of the skin to tan and its propensity to burn were also significantly associated with risk of SCC (OR of 2.9 for severe burn and 3.5 for no tan).