We read with interest the recent article by Hochheiser et al. regarding the economic impact of four multi-gene assays (MGAs) used to make decisions regarding chemotherapy use in women with newly diagnosed estrogen receptor-positive, HER2-negative breast cancer: 21-gene recurrence score (Oncotype DX R ), 70-gene signature (MammaPrint R ), PAM50 (commercial; Prosigna R ) and 12-gene molecular score (EndoPredict R ) [1]. We wish to highlight several deficiencies in the study design and the resultant conclusions.The authors described the variables that were utilized in their cost-effectiveness model, which included two elements related to the risk of distant recurrence according to MGA risk stratification: the 10-year probability of recurrence without chemotherapy (i.e., prognostic performance) and the 10-year relative risk of recurrence with and without chemotherapy (i.e., predictive performance). These values were then applied to decision-impact data (i.e., how testing with each MGA impacted chemotherapy treatment decisions) to model the cost-effectiveness of each MGA. Hochheiser et al. [1] followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to compile all available and applicable decision-impact literature for the four MGAs. However, the authors did not use this same approach to compile literature reporting on the ability of the MGAs to stratify the 10-year risk of distant recurrence.There are several significant issues regarding the values for the prognostic performance of the MGAs that the authors used as inputs to their model. Hochheiser et al. [1] cite a meta-analysis from the Early Breast Cancer Trialists' Collaborative Group [2] as the source of the input prognostic values for the 12-gene molecular score and PAM50 (commercial) score. The authors state that this meta-analysis "provided commonly cited rates for distant recurrence"; however, this citation predates the MGAs and does not contain any molecular data. Therefore, it is not possible to use this meta-analysis to obtain input values for the probability of recurrence without chemotherapy according to MGA risk group for the 12-gene or PAM50 (commercial) scores if the MGAs themselves did not exist yet. As such, the base prognostic variables used for these MGAs are questionable and may be invalid and, by association, so are any conclusions drawn from them.The EndoPredict test result is a combined clinico-molecular score (EPclin) that incorporates tumor size and nodal status with a 12-gene molecular score. Hochheiser et al. [1], used decision-impact data for the EPclin score in their model; however, the base case variables used for the prognostic and predictive performance appear to be for the 12-gene molecular score and not the EPclin score. This is inappropriate for two reasons. First, there is inconsistency within the authors' model regarding the use of the 12-gene molecular score and EPclin score. Second, the EPclin score is the actual test result provided to clinicians for use in treatment decisions and would have ...