Small open studies of patients at high risk for squamous cell carcinoma (SCC) of the skin suggest that oral retinoid use reduces the risk of these tumors. Among patients at lower risk, randomized trials of low doses of retinoids did not demonstrate significant chemopreventive effects. Patients with psoriasis treated with oral psoralen-UVA have a high risk of SCC development. Oral retinoids are used to treat psoriasis. We performed a nested cohort study to assess whether oral retinoids reduce skin cancer risk among patients with psoriasis exposed to psoralen-UVA.

From 1985 to 2000, 135 patients (11.3% of surviving patients in our cohort) used retinoids for at least 26 weeks in 1 year or more. For these 135 patients, we compared each person's SCC and basal cell carcinoma incidence during years of substantial oral retinoid use and other years. We used Poisson regression models to adjust for potential confounders.

In a paired analysis, which compared each patient's own tumor experience while using and not using retinoids, retinoid use was associated with a 30% reduction in SCC incidence (196 SCCs/1000 and 302 SCCs/1000 years of use and no use, respectively; P = .002). After adjusting for other factors associated with SCC risk, the incidence of SCC was significantly decreased during years of substantial retinoid use (incidence rate ratio = 0.79; 95% confidence interval = 0.65, 0.95). Oral retinoid use and basal cell carcinoma incidence were not significantly associated.

In patients with psoriasis treated with psoralen-UVA, systemic retinoid use reduced SCC risk but did not significantly alter basal cell carcinoma incidence.