Skin tumors in photochemotherapy for psoriasis: a single-center follow-up of 496 patients.

BACKGROUND: The significance of oral psoralen photochemotherapy (PUVA) for the development of nonmelanoma skin cancers (NMSC) is still controversial.

OBJECTIVE: We evaluated 496 psoriatics, who received PUVA treatment according to the European PUVA protocol in order to reassess the influence of the cumulative UVA dose on the development of NMSC and to answer the question if there is a UVA threshold dose above which the carcinogenic risk is increased.

METHODS: The study was conducted as a retrospective investigation. All patients were seen personally. Age, sex, skin type, cumulative UVA dose and carcinogenic risk factors (arsenic, X-rays, tar, UVB, methotrexate) were recorded and investigated by marginal (MA) and partial effects analyses (PA) according to the Cox regression model.

RESULTS: In 14 patients (2.8%), one or multiple histologically confirmed NMSC were diagnosed. Nine patients (1.8%) had squamous cell carcinoma (SCC), 5 patients (1.0%) had basal cell carcinoma (BCC). No patient had both types of NMSC. None of the SCC had metastasized. By taking the appearance of BCC and SCC as the endpoint, arsenic [MA: relative risk (RR) = 7.62; PA:RR = 5.36], tar (MA:RR = 4.51; PA:RR = 3.83) and methotrexate (MTX; MA:RR = 4.97; PA:RR = 4.07) appear to produce strong and significant effects (p < 0.05), both in MA and PA. Using the endpoint SCC only, the effect of the natural logarithm of UVA (ln UVA; RR = 2.47), arsenic (RR = 11.2), tar (RR = 9.92) and MTX (RR = 7.1) is significant (p < 0.05) in MA. In PA, only the effect of arsenic (RR = 5.19) is strong and significant (p < 0.05) while the effects of tar (RR = 7.85), MTX (RR = 3.22) and ln UVA (RR = 2.77) are strong but of borderline significance (p = 0.05-0.11). Nonlinear effects of ln UVA on the risk of SCC were far from significant (p > 0.2).

CONCLUSION: PUVA with the European treatment protocol appears to be only a weak carcinogen by itself for SCC with a linear increase in tumor risk but not for BCC development.