The Impact of Environmental Light Intensity on Experimental Tumor Growth.

BACKGROUND/AIM: Cancer research requires for consistent models that minimize environmental variables. 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; however, studies evaluating the differential effect of light intensity during the light phase on tumor growth are lacking.

MATERIALS AND METHODS: The effect of cage face light intensity, as determined by cage rack position was evaluated with two tumor models using the C57Bl/6NHsd mouse and transplantable B16F10 melanoma cells or Lewis lung carcinoma (LLC) 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, and cage face light intensity was measured. Following a two-week acclimation period at the assigned cage position, animals were subcutaneously administered either 1.3×106 B16F10 melanoma cells or 2.5×105 Lewis lung carcinoma cells. Weights of excised tumors were measured following euthanasia 18 days (melanoma) or 21 days (LCC) after tumor cell administration.

RESULTS: Cage face light intensity was significantly different depending on the location of the cage, with cages closest to the light source have the greatest intensity. Mean tumor weights were significantly less (p<0.001 for melanoma; p≤0.01 for LCC) in middle light intensity mice compared to high and low light intensity mice.

CONCLUSION: The environmental light intensity to which experimental animals are exposed may vary markedly with cage location and can significantly influence experimental tumor growth, thus supporting the idea that light intensity should be controlled as an experimental variable for animals used in cancer research.