A Phase II Expansion Study Of Vorinostat In Combination With Idarubicin and Cytarabine For Patients With Acute Myelogenous Leukemia (AML) With FLT3 Molecular Alterations

The combination of vorinostat, idarubicin and cytarabine (IA+vorinostat) is associated with high response rate in patients with newly diagnosed acute myelogenous leukemia (AML) or higher-risk myelodysplastic syndromes (MDS) (JCO 2012;30:2204). In that study, presence of FLT3-ITD was associated with 100% overall response rate (ORR) in 11 patients. To confirm the efficacy of this combination, we extended the phase II study to treat 2 additional cohorts: one for patients with newly diagnosed (untreated cohort) and the other with relapsed and refractory (R/R cohort) AML or higher-risk MDS with FLT3 alteration (both ITD and D835 mutation).

Patients with the above diagnosis, ages 15 to 65 years, with appropriate organ function (measured cardiac ejection fraction ≥ 50%, serum creatinine ≤ 2 mg/dl, total bilirubin ≤ 2 mg/dl, and GPT/GOT ≤ 2.5 x upper limit of normal) whose eastern cooperative group (ECOG) defined performance status ≤ 2 were eligible for the study. Study treatment comprised of vorinostat 500 mg orally three times a day (days 1 to 3), idarubicin 12 mg/m² intravenously (IV) daily x 3 days (days 4 to 6), and cytarabine 1.5 g/m² IV as a continuous infusion daily x 3 - 4 days (days 4 to 7). Patients in remission could be treated with five cycles of consolidation therapy with lower dose combination and up to 12 months of maintenance therapy with single-agent vorinostat.

Untreated cohort included 26 patients, whereas 13 patients were treated in R/R cohort (total 39 patients). Thirty six patients had de novo AML, 1 had de novo MDS and 2 had therapy-related AML. For the R/R patients, the median number of prior therapies was 3 (range: 1-6). The median age of the entire study group was 49 (range: 19-64) and 17 (44%) were male. Among the patients whose cytogenetic result were available, 20 (51%) patients had normal and 15 (39%) had abnormal karyotype. By Medical Research Council (MRC) criteria, 30 (77%) patients had intermediate risk and 9 (23%) had poor risk karyotype. Thirty three (85%) patients had FLT3-ITD only, 4 (10%) had both FLT3-ITD and D835 mutation, and 2 (5%) had D835 mutation only. Seventeen (44%) patients had NPM1 mutation.

In untreated cohort (N = 26), CR and CRp were documented in 21 (80%) and 2 (8%) patients, respectively (ORR = 88%). In R/R cohort (N = 13), overall response (OR) was observed in 4 (30%) patients (CR in 2 [15%] and CRp in 2[15%]). Of those 4 patients who had OR in R/R cohort, 2 patients were refractory to other high-dose cytarabine-based regimen. The median duration of CR or CRp was 9.2 months (range: 0.1-48.4) in untreated cohort and was 2.9 months (range: 1.6-4.7) in R/R cohort. Twelve (46%) patients in the untreated cohort were bridged to stem cell transplant (SCT) while they were in 1^st CR. None of the patients in R/R cohort were bridged to SCT. No difference in response was observed in 1) younger (Age < 60) vs. older patients, 2) normal vs. abnormal karyotype, 3) intermediate vs. poor risk cytogenetics by MRC criteria, 4) presence of RAS mutation, 5) presence of NPM1 mutation, or 6) de novo vs. therapy-related disease.

The median overall survival (OS) was 21.7 months (95% CI: 8.1-35.3) in the untreated cohort and was 4.9 months (95% CI: 0.1-10.4) in the R/R cohort. Early treatment related mortality (defined by the death within 4 weeks of the induction) was documented in 1 (4%) patient in the untreated cohort and 2 (15%) patients in the R/R cohort. Toxicity profiles were similar to that reported in the original phase II study (JCO 2012;30:2204).

Vorinostat in combination with IA provides high response rate and durable remission in previously untreateed AML or higher risk MDS patients with FLT3 alteration but is less effective in patients with R/R disease. Phase III randomized study of IA+/- vorinostat in previously untreated AML patients is ongoing (SWOG S1203).

Off Label Use: vorinostat in MDS and AML. Cortes:Ambit: Research Funding; Astellas: Research Funding; Argo: Research Funding; Novartis: Research Funding.