Effects of oral administration of tea, decaffeinated tea, and caffeine on the formation and growth of tumors in high-risk SKH-1 mice previously treated with ultraviolet B light

Treatment of SKH-1 mice with ultraviolet B light (UV-B, 30 mJ/cm(2)) twice a week for 22-23 weeks resulted in tumor-free animals with a high risk of d eveloping malignant and nonmalignant tumors during the next several months in the absence of further UV-B treatment (high-risk mice). In three separat e experiments, oral administration of green tea or black tea (4-6 mg tea so lids/ml) as the sole source of drinking fluid for 18-23 weeks to these high -risk mice inhibited the formation and decreased the size of nonmalignant s quamous cell papillomas and keratoacanthomas as well as the formation and s ize of malignant squamous cell carcinomas. In one experiment all these inhi bitory effects of tea were statistically significant, whereas in the two ot her experiments many but not all of the inhibitory effects of tea were stat istically significant. The decaffeinated teas were inactive or less effecti ve inhibitors of tumor formation than the regular teas, and adding caffeine back to the decaffeinated teas restored biological activity. Oral administ ration of caffeine alone (0.44 mg/ml) as the sole source of drinking fluid for 18-23 weeks inhibited the formation of nonmalignant and malignant tumor s, and this treatment also decreased tumor size in these high-risk mice.