Protein S and protein C level changes with adjuvant tamoxifen therapy in postmenopausal women

Tamoxifen citrate is a synthetic antiestrogen that provides survival benefit when given as adjuvant treatment in postmenopausal women with breast cancer. Venous thrombophlebitis may complicate tamoxifen treatment at a rate of approximately one per 800 treatment-years. To explore the possible procoagulant effects associated with tamoxifen therapy we evaluated changes in protein S and C activity levels in 58 postmenopausal women with surgically resected breast cancer who were disease-free and participating in a double-blind, placebo-controlled, randomized toxicity study of tamoxifen. The changes in protein C activities for the tamoxifen group (mean level = 113%) compared to those in the placebo group (mean level = 115%) were not significant (p = 0.45). Protein S activity levels increased while protein C activity levels decreased from baseline at 24 months in both tamoxifen and placebo groups. We conclude that the possible thrombophlebitis-promoting effect of tamoxifen in postmenopausal women is unlikely to be explained on the basis of protein S and protein C activity level changes.