Department of Dermatology, Beth Israel Deaconess, Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA

Correspondence: Robert S. Stern, Department of Dermatology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, Massachusetts 02215, USA. Email: rstern@caregroup.harvard.edu

Received 24 September 2002; Revised 4 December 2002; Accepted 4 March 2003; Published online 23 July 2003.

Abstract

Psoralen+ultraviolet A-treated psoriasis patients are at increased risk for nonmelanoma skin cancer. To assess the persistence of cancer risk among patients who have discontinued psoralen+ultraviolet A and the risk of a first tumor with the passage of time, we prospectively studied the incidence in a cohort of 1,380 psoriasis patients treated with psoralen+ultraviolet A.

We observed a total of 27,840 person-years of which 59.4% were considered years without psoralen+ultraviolet. No significant decrease in risk was noted during the first 15 years after psoralen+ultraviolet A was discontinued. Subsequently, the risk of squamous cell carcinoma was reduced (incidence rate ratio=0.79; 95%CI=0.62, 1.01 on treatment vs >15 years off). After 25 years, about 7% of patients with 200 psoralen+ultraviolet A treatments and more than half of the patients with 400 treatments develop at least one squamous cell carcinoma. After 25 years, almost one third of the patients exposed to 200 treatments developed at least one basal cell carcinoma.

In conclusion, substantial exposure to psoralen+ultraviolet A dramatically increases the risk of nonmelanoma skin cancer and prior exposure to psoralen+ultraviolet A remains an important issue in the management of patients because the cancer risk associated with psoralen+ultraviolet A is persistent.