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Acute Myeloid Leukemia |
* Institute of Hematology and Medical Oncology "L. and A. Seràgnoli", S. Orsola-Malpighi Hospital, University of Bologna, Bologna;
° Department of Hematology, University of Brescia;
# Department of Hematology, University of Udine;
@ Department of Hematology,Orbassano,University of Torino;
^ Department of Hematology,University of Siena;
Department of Hematology, Pesaro;
** Novartis-Pharma, Italy
Correspondence: Pier Paolo Piccaluga, MD, PhD, Institute of Hematology and Medical Oncology "L. and A. Seràgnoli", S. Orsola Malpighi Hospital, University of Bologna, Via Massarenti, 9, 40138 Bologna, Italy. Phone: international +39.051.6364043. Fax: international +39.051.6364037. E-mail: pierpaolo.piccaluga{at}unibo.it
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ABSTRACT |
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Key words: imatinib mesylate, acute myeloid leukemia, c-KIT, PDGFRB, targeted therapy.
The treatment of poor risk acute myeloid leukemia (AML), including elderly patients or those with poor performance status, or with refractory/relapsed disease, remains problematic due to the scarce efficacy and high toxicity of conventional chemotherapy.1–5
We investigated the efficacy and toxicity of imatinib in c-KIT+ AML cases. Some authors reported responses in c- KIT+ AML and high-risk myelodysplastic syndromes (MDS).6,7 Nevertheless, whether c-KIT was the actual target in such cases is still unclear. The primary endpoint was the response rate assessment. The secondary endpoints were CR duration, overall survival at 12 months and type, frequency, severity, timing, and relatedness of adverse events (AE).
Thirty-six c-KIT+ AML patients not amenable to conventional chemotherapy were enrolled in an open label phase II study. Patients aged over 18 years, with any FAB but M3 AML refractory or relapsed after conventional chemotherapy, as well as patients with previously untreated AML not conventional chemotherapy were eligible, provided that at least one of the known imatinib targets, PDGFR 
orβ, c-KIT (assessed by flow-cytometry) or BCR-ABL1 (assessed by RT-PCR) was expressed. No core-binding-factor positive patients were enrolled. Treatment consisted of imatinib mesylate at the initial dose of 100 mg/day. If no major toxicity was observed, imatinib dosage was increased every second day up to a maximum of 800 mg/day. Therapy was assumed for at least two months and continued if a clinical response was observed. In cases of clear progression, the treatment could be withdrawn at any time at the physician’s discretion. Clinical response was evaluated according to conventional criteria.8
All the 36 enrolled patients were evaluated for response. Only 1 out of 36 patients obtained a clinical response. She showed a hematologic improvement, with transient platelet increase and temporary transfusion independence. Conversely, Hb, WBC count and bone marrow blasts did not significantly improve. The clinical benefit lasted for approximately 4 months (Figure 1A). Intriguingly, this patient was the only one with expression of PDGFRB. While under treatment, blast cells progressively became PDGFRB negative, until progression occurred (Figure 1). On the contrary, CD117 was expressed and phosphorylated during the entire treatment duration. None of the other 35 patients (97%) responded. Of these patients, 21 (62%) and 7 (21%) interrupted imatinib for disease progression and adverse events respectively. Six out of 36 patients (17%) died during imatinib therapy, due to cerebral hemorrhagic stroke (2), disease progression (2) and multi organ failure (2). The median treatment duration was 31 days (range 2–311), at a median dosage of 600 mg/day (range 200–800). Only 53% of patients assumed imatinib for at least 4 weeks. The other patients withdrew from the study within 4 weeks of therapy due to disease progression, or died within this period while on therapy. The median overall survival was 3 months (0.5–44+) (Figure 1B). Imatinib was overall well tolerated. Treatment outcome and toxicity are summarized in Table 1 and Figure 1C respectively.
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However, whether c-KIT is not a good candidate as therapeutic target in AML or whether imatinib was not able to completely inhibit its function is not known. It is unlikely, however, that D816-c-KIT mutations played a role since these are rare in unselected AML. In our series, responses were not observed despite c-KIT de-phosphorylation during treatment, while the single responder showed p-CD117+ when PLT count increased. Furthermore, other possible targets may be relevant in AML rather than c-KIT, including c-FMS which can be inhibited by imatinib.9,10 On the other hand, the biologic and clinical role of PDGFRB inhibition should also be further investigated in AML.
We conclude that imatinib is not effective as single agent in the treatment of c-KIT+ AML, though further studies might indicate possible indications in specific AML subsets.
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Footnotes |
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Funding: this work was supported in part by AIRC, BolognAIL, FIRB/RFO (Prof. M Baccarani), Fondazione Cassa di Risparmio, and Fondazione del Monte di Bologna e Ravenna grants.
Additional information on this trial are available upon request (pierpaolo.piccaluga{at}unibo.it).
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