Reduced ultraviolet irradiation delays subsequent squamous cell carcinomas in hairless mice

Abstract

Ultraviolet (UV) radiation induces non-melanoma skin cancer (NMSC), and UV prophylaxis is essential to prevent skin cancer. It is unclear whether patients diagnosed with squamous cell carcinomas (SCC) may benefit from reduced UV exposures in terms of delaying the development of new tumors. The objective was to evaluate the significance of discontinued or reduced UV exposure for the development of subsequent skin tumors. Seven groups of mice (n = 175) were irradiated with UV doses of 2 and 4 standard erythema doses (SED) that were continued, reduced or discontinued at the time of appearance of the first skin tumor. The development of new tumors was delayed, corresponding to the degree of reductions in UV dose in an inversely linear manner. Discontinuation of UV doses delayed the median times to the second tumor by 24 days (2 SED, P = 0.0549) and 33.5 days (4 SED, P < 0.0001), and when reduced to 1 SED, the median delays were 18 days (2 SED, P = 0.0469) and 33 days (4 SED, P < 0.0001). The median delay to the third tumor was after UV reduction 47 days (4 SED, P < 0.0001) and 35 days (2 SED, P = 0.151), and after UV discontinuation 49 days (4 SED, P < 0.0001) and 44 days (2 SED, P = 0.111). This suggests that patients with SCC may benefit from reduced UV exposure.