Influence of NPM1 and FLT3-ITD Status On Outcome in Relapsed/Refractory AML Patients with Normal Karyotype and Receiving Salvage Therapy Including Gemtuzumab Ozogamicin (GO).

Abstract 3110

Poster Board III-47

The aim of this study was to investigate the influence of the NPM1/FLT3-ITD status on outcome in relapsed/refractory AML patients with normal karyotype who received a salvage regimen using GO as monotherapy or in combination with other agents.

For this purpose, we analyzed the outcome of 57 AML patients with normal karyotype treated between 2001 and 2009. Patients received GO as monotherapy or in combination with other chemotherapeutic agents at time of relapse (n=36) or in the setting of refractory disease (n=21). There were 26 males and 31 females with a median age of 52 (range, 20-70) years at time of leukemia diagnosis. The FAB distribution included 2, 13, 15, 11, 12 and 1 AML cases from the M0, M1, M2, M4, M5 and M6 subgroups, respectively. Three cases were considered as unclassified. In addition, 5 patients had secondary AML. All patients were CD33 positive with a median CD33 expression level of 98%. As salvage treatment, 46 patients received the MIDAM regimen (GO: 9 mg/m² at day 4 + Cytarabine 1g/m²/12 hours day 1-5 + Mitoxantrone 12 mg/m²/day day 1-3).³ In 2 patients receiving the MIDAM regimen, Mitoxantrone was omitted to avoid cardiac toxicity. Four patients received GO as monotherapy at 9 mg/m² (n=3) or at 6 mg/m² (n=1). The 5 remaining patients received GO 3 to 9 mg/m² combined with other chemotherapeutic agents (Cytarabine + VP16 + GO, n=2; Cytarabine + Idarubicine + GO, n=2; Cytarabine + Amsacrine + GO, n=1). After salvage therapy, 25 patients could proceed and receive consolidation with an allogeneic stem cell transplant.

In this series, all patients could be screened in the blood or bone marrow for mutations in the NPM1 and in the FLT3 gene (ITD mutations) at diagnosis. Numbers of patients according to NPM1/FLT3-ITD status were as follow: (+/−): n=14, (+/+): n=9, (−/−): n=19, (−/+): n=15. The same proportion of refractory patients was observed in the favourable NPM1+/FLT3-ITD- sub-group as compared to the other sub-groups (36%, n=5/14 vs 37%, n=16/43).

With a median follow-up of 23.3 (range, 2.3-94.5) months for surviving patients, OS was 46.5% (95%CI, 33.6-59.9%) at 2 years. CR, relapse and death rates according to NPM1/FLT3-ITD status were as follow: CR: (+/−): 85%, (+/+): 66%, (−/−): 47%, (−/+): 73%, P=NS; Relapses: (+/−): 33%, (+/+): 33%, (−/−): 33%, (−/+): 54%, P=NS; Deaths: (+/−): 28%, (+/+): 78%, (−/−): 58%, (−/+): 66%, P=0.02 Also, the death rate was significantly lower in FLT3-ITD- patients as compared to FLT3-ITD+ cases (45% vs. 71%, P=0.05). OS was significantly higher in the NPM1+/FLT3-ITD- sub-group as compared to other patients (78% vs. 36% at 2 years, P=0.026).

In conclusion, and although this needs to be confirmed in a prospective setting, refractory/relapsed AML patients combining a normal karyotype and a NPM1+/FLT3-ITD- molecular status are likely to remain in a “favorable prognosis” category when receiving salvage therapy. Such information is of major interest for patients counselling and for the design of salvage therapy approaches.