Impact of UVR Exposure Pattern on Squamous Cell Carcinoma-A Dose–Delivery and Dose–Response Study in Pigmented Hairless Mice

Cumulative lifetime ultraviolet radiation (UVR) is an important factor in the development of squamous cell carcinoma. This study examines the impact of UVR exposure pattern on tumor development. Hairless C3.Cg/TifBomTac immunocompetent pigmented mice (n = 351) were irradiated with 12 standard erythema doses (SED)/week, given as 2 SED ×6, 3 SED ×4, 4 SED ×3, or 6 SED ×2 (dose–delivery study) or 0, 0.6, 1.2, 2, 3 or 4 SED ×3/week (dose–response study). All mice were irradiated until development of 3 tumors of 4 mm each. Pigmentation was measured once monthly. In the dose–delivery study, the median time until tumor development was independent of dose fractions. In the dose–response study, higher UVR doses resulted in faster tumor appearance. When the weekly UVR dose was decreased from 12 to 6 SED, the cumulative UVR dose needed for tumor development was reduced by 40%. In conclusion, delivery schedules of a fixed weekly UVR dose did not affect tumor development. When using different weekly UVR doses, longer time to tumor development was observed using lower UVR doses. Lower weekly UVR doses however resulted in lower cumulative UVR doses to induce tumors in hairless pigmented mice.