Suckow, M. A., Wilhite, S., Wolter, W. R. et al. 2013. Effect of light intensity as determined by cage rack position on tumor growth in a mouse model of melanoma. American Association for Laboratory Animal Science [AALAS] Meeting Official Program, 670 (Abstract #P178).

Within the typical laboratory animal housing facility, animals may be exposed to varying intensities of light as a result of cage type, cage position, light source, and other factors. While evidence exists that light contamination during the dark phase of the light cycle can impact the growth of tumors in laboratory rodents, no studies evaluating the differential effect of light intensity during the light phase on tumor growth have been published. The effect of cage face light intensity as determined by cage rack position was evaluated in the C57Bl6 mouse model of melanoma using transplantable B16F10 cells. Animals were housed in individually ventilated cages placed at the top, middle, or bottom of the rack in a diagonal pattern so that the top cage was closest to the ceiling light source, 10 mice per light exposure group. Cage face light intensity was measured with a digital illuminance meter to be 3.1 lx (bottom), 169.0 lx (middle), and 320.8 (top) lx. Following a 2-wk acclimation period at the assigned cage position, animals were administered 1.3 × 106 B16F10 melanoma cells subcutaneously. Tumor diameters of mice were measured with a digital caliper at days 12, 15, and 18. ANOVA analysis of tumor diameters showed the middle light intensity group to have significantly smaller (P < 0.001) tumors on every day they were measured compared with high and low light groups. Likewise, when mice were euthanized 18 d after tumor cell administration, mean tumor weight was significantly (P <0.001) less in middle light intensity mice (1.21 ± 0.79 g ) compared with high (6.32 ± 2.74 g) and low (5.98 ± 3.25 g) light intensity mice. In summary, the light intensity to which animals are exposed may vary markedly with cage location and can significantly influence experimental tumor growth, thus supporting the idea that light is an important experimental variable.