All-Trans Retinoic Acid and Gemtuzumab Ozogamicin as Adjunct to High-Dose Cytarabine-Based Salvage Therapy in Primary Refractory Acute Myeloid Leukemia: Results of AMLSG 05-04 Trial.

Background: Patients with primary refractory acute myeloid leukemia (AML) have a dismal outcome. Only allogeneic stem cell transplantion (SCT) currently offers the chance of cure to these patients. In order to improve outcome after allogeneic SCT, one important prerequisite is to increase response rates prior to SCT.

Aims: To evaluate the impact of all-trans retinoic acid (ATRA) and gemtuzumab ozogamicin (GO) given as adjunct to high-dose cytarabine-based salvage therapy in younger adult patients with primary refractory AML on achievement of response. Consecutive allogeneic SCT was intended in all patients.

Methods: Main inclusion criteria of the AMLSG 05-04 trial (NCT00143975) were

• refractory AML following one cycle of ICE (idarubicin, cytarabine, etoposide); and

• age 18 to 60 years.

Dose and schedule of the GO-A-HAM regimen were as follows: GO 3mg/m², day 1; cytarabine 3g/m² bid., days 1–3; mitoxantrone 12mg/m², days 2,3; ATRA 45mg/m², days 3–5, 15mg/m² days 6–28. Primary endpoint of the study was CR rate. Safety endpoints comprised early / hypoplastic (ED/HD) death rate, liver toxicity CTC grade 3–5, and rate of veno occlusive disease (VOD) after allogeneic SCT.

Results: Between September 2004 and June 2007, 94 patients (median age, 48 yrs; range, 22 to 62) were enrolled. Distribution of cytogenetics was as follows: adverse, n=29 [abn(3q), −5/5q-, −7/7q-, abn(12p), abn(17p), complex]; other n=57 [core binding factor (n=3), cytogenetically normal AML (n=37), various aberrations (n=18)]. FLT3-ITD was present in 18 (22%) of 82 analyzed patients. Response to GO-A-HAM was as follows: CR, n=28 (30%); CRi, n=19 (20%); PR, n=11 (12%); refractory disease (RD), n= 34 (36%); and ED/HD, n=2 (2%). In a logistic regression analysis for achievement of CR, the only significant variable was adverse cytogenetics (OR 0.34, p=0.02). The rate of severe liver toxicity was 0%, the incidence of neutropenic fever was 52%, platelet and neutrophil recovery times from start of treatment were 21 and 22 days, respectively. Following GO-A-HAM, allogeneic SCT was actually performed in 60 patients (64%): matched related (n=14) or unrelated donor (n=42); haploidentical related donor, n=4. All SCT were performed within 3 months after GO-A-HAM, intermediate/severe VOD developed in 5 patients after SCT (9%, 95%-confidence interval (CI) 4–19%), mild VOD in 3 patients. Survival analyses revealed that patients with adverse cytogenetics and/or FLT3-ITD (n=45) had a significantly (p=0.001) inferior overall survival after one year of 38% compared to all other patients (n=39) of 81%. The proportions of patients receiving an allogeneic SCT were similar in both groups (68% and 66%, respectively).

Conclusions: The GO-A-HAM regimen is feasible and effective as salvage therapy. However, cytogenetics still remains the most significant variable for achievement of response. Allogeneic SCT after GO-A-HAM was not associated with an increased VOD-rate.