Post-Transplant Maintenance With The Deacetylase Inhibitor Panobinostat In Patients With High-Risk AML Or MDS: Results Of The Phase I Part Of The Panobest Trial

12 pts (11 AML, 1 MDS), median age of 52 years (21-62) were enrolled. PAN was started within a median of 73 days (60-126) after HSCT, which was performed with active disease (n=11) or in CR2 (n=1). The RP2D was determined to be 20 mg TIW based on one DLT (fatigue grade 3) at 20 mg and two DLTs (nausea/emesis and colitis grade 3 each) at 30 mg. Grade 2-4 adverse events (AEs) were reported in 10 out of the 12 pts (83%). Grade 3/4 AEs included hematologic toxicity (50% of pts), laboratory alterations (33%), gastrointestinal symptoms (25%), fatigue, pulmonary infection (17% each), sepsis, herpes stomatitis, diabetes, syncope, deep vein thrombosis and pulmonary embolism (8% each). Toxicity was reversible and required at least one PAN dose reduction in 3 pts. Acute GvHD grade 2 (1 pt) and 3 (2 pts) was responsive to steroids in 2 pts or salvage therapy in 1 pt. Four pts developed mild (n=3) or moderate (n=1) chronic GvHD. To date, 5 pts have completed one year of PAN and 2 pts remain on treatment (days 238, 290). Five pts discontinued treatment prematurely after 10-217 days due to grade 3 toxicities (n=4) or AML relapse (n=1). With a median follow up of 579 days (129-911), 11/12 pts are alive and 10/12 in continuous CR after HSCT. Seven pts received prophylactic donor lymphocyte infusions (DLIs, 1-5 doses of 0.1-20x10⁶ CD3⁺ cells/kg). Immunophenotyping revealed no impact of PAN on absolute T reg numbers (9 pts), but a significantly reduced proportion of CD4⁺CD25⁺⁺CD127^dim/- T reg to CD3⁺CD4⁺ T helper (Th) cells by day 8 after 3 doses of PAN (mean±SEM: 14.6±2.6 vs. 9.6±1.2%, p value of t test =0.03). While Treg/Th proportion continuously decreased in pts with ongoing CR, it again increased after PAN discontinuation or remained stable under PAN treatment in both relapsing patients. Outcome of the study population was compared with a historical cohort of 29 consecutive pts with active AML transplanted in Frankfurt in 2000-2009. Both cohorts were similar in age, gender, disease stage or BM blasts at time of HSCT, donor type and use of DLIs. In a landmark analysis including all pts who were in CR and without severe GvHD on day 73 after HSCT, probabilities for DFS and OS at 18 months after HSCT were 83±11% vs. 55±9% (p=0.145, log-rank test) and 92±8% vs.66±9% (p=0.085) in the PANOBEST vs. historical cohort (Fig 1).