Figure 1.

Activity of tamoxifen in human tumor xenografts in mice. A) MDA-MB-435 estrogen receptor–negative melanoma xenografts. B) MDA-MB-361 estrogen receptor–positive breast cancer xenografts. Cells of both lines were implanted orthotopically into the mammary fat pad of athymic nu/nu NCr mice (Animal Production Program, NCI-Frederick), and treatment was initiated when the tumors reached 150–175 mg in size. The MDA-MB-361 tumor-bearing mice were treated weekly with estradiol cypionate (20 μg per mouse) to support tumor growth. Exogenous estradiol is not required for progressive growth of MDA-MB-435 xenografts. For both studies, the vehicle control was 100% sesame oil given by oral gavage once daily for 20 days (n = 20 mice). Tamoxifen was administered by oral gavage once daily for 20 days at a dose of 45, 22.5, or 11.25 mg/kg (n = 10 mice per dose). Individual tumor weights were calculated as weight in mg = (length × width²)/2. Data are plotted as median tumor weight ± the 95% confidence interval of the median.