One thousand and forty people aged 40 years and over, 616 (59.2%) of whom had solar keratoses, were followed for 12 months. Two hundred and twenty-four people (36.4%) had a spontaneous remission of at least one of their solar keratoses. A total of 485 lesions (25.9%) underwent spontaneous remission out of the 1873 lesions that were present at the first examination of these 224 people. There was no significant difference between the number of lesions present at the initial examination in those who had a spontaneous remission compared with those who did not. There was a 21.8% increase in the total number of solar keratoses in the 1040 people studied in the 12-month period, due to new lesions forming at the same time as remissions were occurring. The incidence rate of squamous cell carcinoma occurring in the people with solar keratoses was 0.24% for each solar keratosis present at the original examination. With a substantial proportion of solar keratoses remitting spontaneously, plus the low rate of malignant transformation and the low potential for metastasis to occur from squamous cell carcinoma arising in a solar keratosis, the rationale of treating all solar keratoses appears questionable.

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Six thousand four hundred sixteen people aged 40 years and over from three different locations in Victoria (Australia) were examined on the hands, forearms, head, and neck for the presence of solar keratoses and basal (BCCs) and squamous cell carcinomas (SCCs). Analysis of the relationship between these tumors revealed that the factors which predicted the likelihood of developing a solar keratosis were essentially the same as those that predicted the likelihood of developing a BCC and/or an SCC. These were age, sex, years of residence in Australia, indoor or outdoor occupation, tanning ability, propensity to sunburn, and location of residence. The presence of a coexisting solar keratosis was necessary for the development of an SCC in contrast to the development of a BCC. The findings suggest that unlike BCCs, the majority of SCCs in light-exposed areas may arise from preexisting solar keratoses. Whereas the prevalence of BCCs and SCCs was relatively constant in the three locations, the prevalence of solar keratoses differed markedly in direct relation to the degree of isolation. This suggests that solar keratoses are a more sensitive indicator of sunlight exposure than invasive carcinoma.

No abstract