OBJECTIVES: Expenses for innovative therapy companion diagnostics (CD) are not covered by the sole payer of health care services in Bulgaria. They are paid for out of pocket or the cost is borne by external treatment access program. Patients and health administrators are advocating for extending coverage for CD. This study uses the payer's perspective and aims at estimating the budget impact of extended reimbursement of CD for innovative solid tumor therapies. METHODS: Incidence and prevalence of solid tumors and the respective genetic markers were obtained from the cancer registry and scientific literature. Medication DDD prices, dose regimens and the average length of treatment were calculated based on the official EMA product specification. The reimbursement sums for innovative therapies, requiring CD, were collected from the National Health Insurance Fund (NHIF). CD test prices were acquired from leading commercial companies in country. The cost of diagnosing one mutation was calculated by allocating the cost for exhaustive investigation of all cancer patients, who present at clinic, to the ones with mutation status and eligible for the respective innovative product. In order to estimate the BI, percentage growth in the cost of single patient treatment course was calculated first, followed by estimating the total reimbursement sum increase for treating newly diagnosed patients. RESULTS: In 2015, EUR 38.3 million were paid by NHIF, covering 12 innovative medications in four cancer types. The projected additional expenditure for covering CD for 8 248 eligible cancer patients can reach EUR 3.1 million per year. Consequently the percentage increase in the cost of single patient treatment course ranges from 0.68% to 24%. CONCLUSIONS: Extending CD testing coverage for innovative medications for solid tumors would not only load the NHIF’s bill but also double the yearly expense for treatment of eligible patients with certain types of cancer.