OBJECTIVES: While there are several instances of products gaining expanded indications from secondary treatment to primary treatment/prevention, in some cases, expanded indications appear to buffer the drug utilization from competitors. However, the extent to which the later expanded indications impact the utilization of the product across the lifecycle, including following loss of exclusivity, is not well understood. The objective was to examine the prescribing volume of a drug throughout its lifecycle in conjunction with the uptake of a novel class of drugs launched for similar indications to examine the impact of the expanded primary treatment/prevention indications on competition. METHODS: Tamoxifen and the aromatase inhibitors letrozole and anastrozole were selected as case products. All three drugs are FDA indicated for the treatment of advanced breast cancer, yet tamoxifen is the only drug of the group FDA indicated for the primary prevention of breast cancer. From January 1992 to April 2010 the volume of prescriptions (TRx) was collected monthly using SDI’s VONA database and grouped according to class sales by active molecule. RESULTS: Generic sales of tamoxifen maintained a high level after the 1998 approval for the primary prevention indication of “reduction in breast cancer incidence in high risk women” despite competition within active breast cancer treatment indications from the aromatase inhibitors.  While, the aromatase inhibitors launched in the mid-1990s, their utilization did not begin to encroach on total tamoxifen prescriptions until the expiration of exclusivity for tamoxifen’s prevention indication in 2003. CONCLUSIONS: This preliminary analysis shows that the strategy of obtaining a later primary prevention indication may help maintain utilization of a compound across the lifecycle. The hypothesis that a prevention indication expansion could mitigate competition should be further examined among products where primary prevention and primary treatment indications have distinctly different dosages and/or branding and where the additional indication is protected by extended exclusivity.