OBJECTIVES:

We estimated the cumulative life years saved and recurrences avoided after incorporating trastuzumab as therapy for metastatic breast cancer (MBC) in 1999 and early breast cancer (EBC) in 2006 in the United States.

METHODS:

We constructed a model to estimate population survival and recurrence among patients who received trastuzumab each year, and compared it to a counterfactual model in which trastuzumab treatment was not available. We incorporated US population counts, the age-, year-, and nodal status-specific incidence rates of HER2+ EBC, the age- and year-specific rates of de novo MBC, recurrence rates in HER2+ EBC, and year-specific trastuzumab utilization rates in EBC and MBC. Women with low-risk, node-negative EBC were excluded. The risk of recurrence with and without trastuzumab were based on 10-year trial data. Recurrences were estimated for 15 years after diagnosis by carrying the year 10 rate forward. Survival after local and regional recurrences was estimated using the 5-year relative survival for HER2+ EBC. In MBC, the survival estimates with and without trastuzumab were pooled across seven studies. Uncertainty intervals (UI) were estimated using Monte Carlo simulation with 500 replicates.

RESULTS:

We estimate that between 2006-2019, trastuzumab use in HER2+ EBC led to the avoidance of 4,500 (95% UI 2,900-6,200) loco-regional and 10,100 (95% UI 6,400-13,800) distant recurrences. This in turn resulted in an incremental 407,900 (95% UI 291,800-528,500) life years saved compared to projected survival with chemotherapy alone. In HER2+ MBC from 1999-2019, there were 72,300 (95% UI 68,300-76,900) women with de novo or recurrent metastatic cancer treated with trastuzumab, leading to an additional 155,200 (95% UI 144,900-166,100) life years relative to projected survival with chemotherapy alone.

CONCLUSIONS:

Trastuzumab has substantially increased the years lived, and reduced recurrences for women with HER2+ MBC and EBC in the United States.