OBJECTIVES: For HER2+ breast cancer patients, initiating the adapted treatment at an early stage increases the chance of survival. Between 2007 and 2014, quality of HER2 testing improved significantly, leading to lower rates of error on HER2 status. We developped a model to evaluate the public health impact of HER2 testing quality improvement since 2007. METHODS: To determine the impact of HER2 testing quality improvement over years, we used a standardized 5-step methodology: 1) thesis statement of the purpose of the project and the criteria to measure the value of an offer, 2) decision tree, 3) patient flow, 4) cost evaluation, 5) communication to stakeholders. For HER2 testing, considering costs and life saved as outcomes, we built a decision tree in order to describe the patient flow of patients diagnosed with breast cancer according to HER2 testing and treatment patterns. Two simulations were conducted for year 2007 and 2014 according to HER2 testing improvement. Testing costs, medical staff and supply costs were considered. RESULTS: Yearly, more than 48,700 malignant breast cancers (in situ not included) are diagnosed in France. In 2007 HER2 testing errors varied between 10% to 17% for false positive and between 4% to 8% for false negative respectively. These rates declined in 2014 to 7%-10% for false positive and 2%-4% for false negative respectively. This improvement of HER2 testing quality resulted in more patients receiving Herceptin at adjuvant stage. Consequently, over the 7 last years this led to annual increase of around 160-330 lives saved and a global decrease of €10M for drug spending. CONCLUSIONS: As targeted therapies’ offer increases more and more in cancer treatment, besides treatment efficacy, it appears crucial to continue optimizing patients profiling with performant testings relying on national quality control insurance. Education, recommendations and good practices workflow are mandatory