In addition to photodamage, excess exposure to the sun can result in solar keratoses, characterized by prominent red or flesh-coloured, warty lesions. These premalignant lesions show histological variation in cell size, nuclear heterogeneity and loss of polarity. lt is therefore considered that a small proportion may eventuate into squamous cell carcinoma.

A number of trials have been undertaken to assess the effects of tretinoin in the treatment of patients with solar keratosis. Over the last 6 years, a total of 1265 patients have been evaluated in double-blind studies at 31 different centres and treated with 0.05% or 0.1% cream for periods of up to 15 months. In all cases, the diagnosis of solar keratosis was confirmed by histological examination at the start of the trial. The efficacy parameters used to evaluate the treatment were lesion count, investigators' global evaluation and patients' self-assessment. Analysis of the data showed that treatment with 0.1% tretinoin cream applied twice daily for 6 months was the most effective treatment, resulting in a significant (P<0.001) reduction in solar keratoses compared with vehicle; reductions in lesions in the tretinoin and vehicle treatment groups were 56% and 41%, respectively. Clinical evaluation also showed that tretinoin was significantly( P<0.001) superior to vehicle, with an excellent or good response being reported in 73% and 40% of cases, respectively. lt is noteworthy that there was a relatively high response rate in the control, vehicle-treated group, as has been observed in other studies. A possible explanation for this is thạt the patients were in structed to apply sunscreens and to avoid exposure to the sun.

As in the studies performed to assess the use of tretinoin for the treatment of photodamage, the cutaneous side-effects of tretinoin were well tolerated when used for the treatment of solar keratoses. Only eight of the 455 patients had to withdraw from treatment, although 88 patients reduced the application frequency of 0.1% tretinoin cream because of local irritation.

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