AbstractProteasome (PIs) and hystone deacetylase inhibitors (HDACis) have previously shown synergistic activity in the treatment of relapesed/refractory multiple myeloma (RRMM) patients. In this phase 1 study, we combined carfilzomib, a second generation PI, with panobinostat, a HDACi, to determine the maximum tolerated dose (MTD) of the combination (CarPan) and assess safety and efficacy among RRMM patients. Thirty-two patients (median of 4 prior lines of therapy) were enrolled. The MTD was carfilzomib 36 mg/m² (on days 1, 2, 8, 9, 15, and 16) and panobinostat 20 mg (TIW, 3 weeks on/1 week off, every 28 days), administered until progression. At the MTD, the most common grade 3/4, treatment-related adverse events were thrombocytopenia (41%), fatigue (17%), and nausea/vomiting (12%). The objective response rate (ORR) and clinical benefit rate were 63% and 68%, respectively. Median progression-free survival (PFS) and overall survival (OS) for the entire population were 8 and 23 months, respectively. No differences in terms of ORR (55% vs. 57%), median PFS (months 8 vs. 7 months) and OS (24 vs. 22 months) were observed between bortezomib-sensitive and -refractory patients. CarPan proved to be a safe and effective steroid-sparing regimen in a heavily pre-treated population of MM patients. (Trial registered at ClinicalTrial.gov: NCT01549431)