OBJECTIVES: The germline BRCA1/2-mutation-positive population in breast cancer has long been identified, but is not well characterized in epidemiological research. PARP inhibitors are a class of drugs in development for germline BRCA1/2-mutation-positive breast cancer. This study sought to provide germline BRCA1/2-mutation-positive breast cancer epidemiology to facilitate the generation of a market forecast for PARP inhibitors across 15 European countries. METHODS: Using peer-reviewed sources, we determined the proportion of germline BRCA1/2-mutation-positive breast cancer cases by molecular subtype. We then applied this proportion to the Decision Resources Group (DRG) breast cancer incident cases and metastatic drug-treatable populations by subtype, across the countries under study. We used interviews with breast cancer experts and secondary market research to model patient progression between lines of metastatic treatment. We used database pricing sources to estimate the cost of PARP inhibitor treatment. RESULTS: We estimate that 4% of newly diagnosed breast cancer cases are BRCA-mutation-positive, with the greatest prevalence of this mutation (14%) occurring among triple-negative (HR-/HER2-) patients in the 15 European countries under study. The triple-negative subtype accounts for 50% of first-line metastatic patients with BRCA mutations. Our findings indicate that over 3,900 BRCA1/2-mutated breast cancer patients will be diagnosed and eligible for treatment across the 15 markets under study in 2017. If PARP inhibitors effectively penetrate adjuvant and metastatic treatment settings, sales of these agents could exceed US$ 400 million across the 15 countries considered in 2027. CONCLUSIONS: Triple-negative patients account for the majority of diagnosed stage I-III (44%) and metastatic (50%) BRCA1/2-mutation-positive breast cancer cases. Lower numbers of BRCA1/2-mutated breast cancers can be found in the remaining three subtypes, however the total size of this population holds the potential to support healthy market sales.