Summary: Sunlight Exposure, Pigmentation Factors, and Risk of Nonmelanocytic Skin Cancer
II. Squamous Cell Carcinoma

Squamous cell carcinoma (SCC) of the skin is a common cancer in white populations, and the incidence appears to be increasing. Sun exposure is thought to be the most important environmental risk factor for the disease, and a number of studies have confirmed this association, without assessing how character, duration and timing of exposure relates to risk. Age is also strongly associated with risk.

The purpose of this study sunlight_ii.pdf was to investigate the relationship of squamous cell carcinoma to individual solar UV exposure, after controlling for phenotype and pigmentary factors. The results show:

• An elevated risk of squamous cell carcinoma among subjects:
  • With light skin and red hair.
  • Who burn rather than tan when first exposed to the sun, and are unable to develop a tan even after a week or more of exposure.
• Subjects whose mothers were of Southern European extraction - Italian, Portuguese, Spanish or Greek - had a reduced risk of SCC compared to those with mothers of English, Celtic and Scandinavian origin.
• Freckling in childhood appears to increase the risk of SCC.
• Two or more very severe burns in childhood, causing pain for two days or longer, markedly increased the risk of SCC.
• A strong trend toward increased risk with chronic occupational exposure in the ten years prior to diagnosis.
• Very severe burns once or more per year in the ten years prior to diagnosis indicated a ten-fold elevation of risk.
• Sunburn frequency in the intermediate decades of adult life (20-29, 30-39, etc.), showed no association with SCC.
• There was no relationship between degree of tanning and risk of SCC.

These results reflect previous study findings, and suggest people with light skin, blond or red hair, who tend to burn rather than tan, are at greater risk of SCC. A propensity to freckle has also been reported as more common in individuals with SCC. Another study found a history of severe sunburn is characteristic of patients with SCC. In addition, one other study reported Southern European origin reduces risk.

Other evidence implies the appearance of squamous cell carcinoma may be related to sunlight exposure just prior to diagnosis. Some actinic keratoses are precursor lesions of SCC, and recent sun exposure is connected to their development. Actinic keratoses sometimes disappear without treatment in people who limit solar exposure, suggesting that the progression to malignancy requires continued exposure to relatively high doses of UV light. If this hypothesis is true, subjects with SCC would likely demonstrate higher UV exposure in the years immediately prior to diagnosis, as was the case in this study.

These results require confirmation in other studies, but suggest late stage solar exposure may be important in accounting for squamous cell carcinoma.

(This study was conducted in conjunction with a companion investigation of basal cell carcinoma of the skin.)

You can refer to the complete journal article for additional details on the:

• Study design, methods and materials.
• Data collected during the study.
• Comments on interpreting the data.