Table 2.

Stimulatory effects of topical applications of caffeine on the formation of mitotic cells with caspase 3–positive staining in skin tumors of high-risk mice previously treated with chronic UVB

TreatmentNo. of nontumor areas or tumors examinedNo. of cells examinedPercent of cells with mitosisPercent of cells with both mitosis and caspase 3–positive stainingPercent of mitotic cells with caspase 3–positive staining
Nontumor areas
 Acetone370123,0000.009 ± 0.0010.001 ± 0.00111
 Caffeine27192,0000.008 ± 0.0010.001 ± 0.00113
 Percent change−11018
Keratoacanthoma
 Acetone202882,0000.351 ± 0.0230.023 ± 0.0057
 Caffeine121426,0000.316 ± 0.0270.071 ± 0.013a22
 Percent change−10209214
Squamous cell carcinoma
 Acetone33555,0000.402 ± 0.0460.026 ± 0.0066
 Caffeine10110,0000.330 ± 0.0330.081 ± 0.034a25
 Percent change−18212317

NOTE: Female SKH-1 mice (7–8 weeks old) were irradiated with UVB (30 mJ/cm2) twice a week for 20 weeks and UVB treatment was stopped. Three weeks later, these tumor-free high-risk mice were randomized and divided into 2 groups (30 mice per group) and treated topically with 100 μL acetone or with caffeine (6.2 μmoles) in 100 μL acetone once daily 5 days a week for 18 weeks. Caspase 3–positive cells were determined immunohistochemically. The percentage of mitotic cells with caspase 3–positive staining in the tumors was analyzed. The entire areas of all tumor sections were examined. Nontumor areas were at least 1 cm away from tumors. Each value represents the mean ± SE.