First do no harm: extending the debate on the provision of preventive tamoxifen

The Breast Cancer Prevention Trial (BCPT-P-1) demonstrated that tamoxifen c ould reduce the risk of invasive breast cancer in high-risk women by 49%, b ut that it could also increase the risk of endometrial cancer, vascular eve nts and cataracts. This paper provides an estimate of the net health impact s of tamoxifen administration on high-risk Canadian women with no prior his tory of breast cancer. The results of the BCPT-P-1 were incorporated into t he breast cancer and other modules of Statistics Canada's microsimulation P Opulation HEalth Model (POHEM). While the main intervention scenario confor med as closely as possible to the eligibility criteria for tamoxifen in the BCPT-P-1 protocol, 3 additional scenarios were simulated. Predicted absolu te risks of breast cancer at 5 years of 1.66%, 3.32% and 4.15% were calcula ted for women 35 to 70 years of age. When the BCPT-P-1 results were incorpo rated into the simulation model, the analysis suggests no increase in life expectancy in this risk group. Tamoxifen appeared to be beneficial for wome n with a 5-year predicted risk of 3.32% or greater. The results of these si mulations are particularly sensitive to the reduction in mortality observed in the BCPT-P-1, as well as being sensitive to other characteristics of th e simulation model. Overall, the analysis raises questions about the use of tamoxifen in otherwise healthy women at high risk of breast cancer. (C) 20 01 Cancer Research Campaign.