[Colon carcinogenesis in rat vs. variable light].

The effect of lighting and melatonin treatment on 1,2 dimethylhydrazine (DMH)-induced colon carcinogenesis was investigated in rats. There was a direct correlation between constant lighting, on the one hand, and the rate of the process, on the other, and an inverse one between light deprivation and melatonin treatment. That presented as changes in rate of tumorigenesis, number of tumors per animal, adenocarcinoma cell differentiation grade, invasiveness and proliferative rate. Our results point to light duration as a significant factor of colorectal cancer progression.