The rheumatoid arthritis treatment response was investigated by the inventors using sera samples collected from RA patients receiving the methotrexate (MTX) / etanercept (ETA) treatment. The clinical efficacy was evaluated using the DAS28 score after 6 months of treatment according to the EULAR response criteria. Two cohorts of patients were investigated, the first is for identification of the combination of biomarkers, and the second one is for validation. Using the first cohort, the inventors performed a differential analysis between responder and non responder samples and revealed 12 differentially expressed serum biomarkers according to patient response. The inventors then used the combination of biomarkers to build a Random Forest statistical model to predict the patient´s response. The inventors also validated the model by a blind test on a panel of patients. The inventors also validated the predictive biomarkers in peripheral blood mononuclear cells from the second cohort.