AbstractThe search for biomarkers based on the mechanism of drug action has not been thoroughly addressed in the therapeutic approaches to multiple myeloma (MM), mainly because of the difficulty in analyzing proteins obtained from purified plasma cells. Here, we investigated the prognostic impact of the expression of 12 proteins involved in the mechanism of action of bortezomib, lenalidomide, and dexamethasone (VRD), quantified by capillary nanoimmunoassay, in CD138-purified samples from 174 patients with newly diagnosed MM treated according to the PETHEMA/GEM2012 study. A high level of expression of 3 out of 5 proteasome components tested (PSMD1, PSMD4, and PSMD10) negatively influenced survival. The 5 analyzed proteins involved in lenalidomide’s mode of action were associated with time to progression (TTP); low levels of cereblon and IRF4 protein and high levels of Ikaros, AGO2, and Aiolos were significantly associated with shorter TTP. Although the glucocorticoid receptor (GCR) level by itself had no significant impact on MM prognosis, a high XPO1 (exportin 1)/GCR ratio was associated with shorter TTP and progression-free survival (PFS). The multivariate Cox model identified high levels of PSMD10 (hazard ratio [HR] TTP, 3.49; P = .036; HR PFS, 5.33; P = .004) and Ikaros (HR TTP, 3.01, P = .014; HR PFS, 2.57; P = .028), and low levels of IRF4 protein expression (HR TTP, 0.33; P = .004; HR PFS, 0.35; P = .004) along with high-risk cytogenetics (HR TTP, 3.13; P < .001; HR PFS, 2.69; P = .002), as independently associated with shorter TTP and PFS. These results highlight the value of assessing proteins related to the mechanism of action of drugs used in MM for predicting treatment outcome.