OBJECTIVES Several multigene prognostic and predictive tests have recently been launched. The 21-gene assay (OncotypeDX®), a validated gene expression profiling test that predicts the likelihood of adjuvant chemotherapy benefit in patients with early stage breast cancer, was found to be cost-effective and recommended in several guidelines. Its use in clinical practice in France is limited because of the absence of reimbursement. This study aims to determine if the utilisation of the 21-gene assay in private hospitals would provide good value for money from a collective perspective in France and whether hospitals can afford using the test under the current payment system. METHODS A multicenter retrospective study was conducted to estimate the cost of adjuvant chemotherapy from societal and national insurance perspectives. The resulting estimate was used as an input of a Markov model to assess the cost-effectiveness of the 21-gene assay from the French collective perspective and the economic impact of the test on the revenue in private hospital organizations. RESULTS The cost of adjuvant chemotherapy in private hospitals was estimated at €8,218 per patient from the national insurance perspective (€10,305 from the societal perspective). The 21-gene assay was found cost-effective compared to standard practice and cost-saving with inclusion of productivity costs. The absence of reimbursement involves a deficit for private hospitals of €3,200 per patient tested. CONCLUSIONS Providing the 21-gene assay in French private hospitals would be cost-effective in the French collective perspective. In the absence of reimbursement from primary payers, some private hospitals may cover the costs of companion diagnostics to improve their attractiveness, but the test will be underused, thus depriving patients from a technology that could improve their quality of life and using resources that could be freed up for other patients.