OBJECTIVES: Triple negative breast cancers (TNBC) with a BRCA1-like profile may benefit from high dose alkylating chemotherapy (HDAC). This study examines whether treating TNBC with personalized HDAC based on BRCA1-like testing can be more cost-effective than current clinical practice. Additionally we estimated the minimum required prevalence of BRCA1-likeness and the required positive predictive value (PPV) for a BRCA1-like test to render this strategy cost-effective. METHODS: Our markov model compared the outcomes of treating TNBC women with personalized HDAC based on BRCA1-like testing vs. current clinical practice from a societal Dutch perspective and a 20-year time horizon. From our base-case model we assessed: 1) the incremental number of respondents; 2) the incremental number of Quality Adjusted Life Years, 3) the incremental costs, and 4) the incremental cost-effectiveness ratio (ICER). We performed one-way sensitivity analysis (SA) of all model parameters, and two-way SA of prevalence and PPV. Data were obtained from a current trial (NCT01057069), published literature and expert opinions where necessary. RESULTS: Based on our base-case analysis with 68% BRCA1-like prevalence, 100% PPV, and costs of € 164 / test, treating TNBC according to BRCA1-like testing would be cost-effective (€16.192/QALY). One-way SA on the prevalence and PPV demonstrated that only the PPV drives the ICER changes. In two-way SA, the lower bound for the two parameters was: prevalence 39.6% and PPV 46.4%. Regardless of prevalence, at PPVs > 46.4% BRCA1-like testing was always cost-effective. CONCLUSIONS: Treating TNBC with personalized HDAC based on BRCA1-like testing is expected to be cost-effective at a minimum PPV of 46%. This information can help test developers in decisions on further research and development