Combination of cyclophosphamide and cytarabine as induction regimen for newly diagnosed adult acute myeloid leukemia

Abstract Optimizing the induction therapy of acute myeloid leukemia (AML) may improve the remission rate and reduce the risk of relapse, thereby extend survival. Cyclophosphamide (CTX) shows benefit in treating relapsed and refractory AML patients, but it has not been reported in first‐line induction regimens. To assess the efficacy and safety of CTX and moderate‐dosage cytarabine (Ara‐C) as induction chemotherapy in newly diagnosed adult AML, 40 patients were enrolled to receive CTX (20 mg/kg/d) for 4 consecutive days and Ara‐C for 3 (1 g/m2 q12h, CA4+3) or 5 (1 g/m2 qd, CA4+5) days. With one course of induction chemotherapy, the overall response rate and the complete remission rate (CR) was 82.5% (33/40) and 77.5% (31/40), respectively. The expected 5 years overall survival and relapse‐free survival was 64% in patients experienced CR and fulfilled consolidation therapy. The neutrophil and platelet recovery time were 17 (range, 10–20) days and 16.5 (range, 12–30) days in the CA4+3 group, faster than that of 20 (16‐36) days and 20 (14‐36) days in the CA4+5 group (P = .006 and P = .006). The cyclophosphamide and cytarabine (CA) regimen was generally safe and had reversible adverse effects. The patients who failed to respond to the CA regimen did not benefit from a second course of other traditional induction chemotherapy either. In conclusion, the combined regimen of CTX and Ara‐C represents a promising therapeutic approach to induce the first CR of newly diagnosed adult AML.


Treatment protocols
CTX was administered at 20 mg/kg/d for 4 consecutive days in both arms. Ara-C was administered at 1 g/m 2 every 12 hours for 3 consecutive days in CA4+3 protocol, and 1 g/m 2 once per day for 5 consecutive days in CA4+5 protocol. The patients were randomly assigned to CA4+3 or CA4+5 protocols at a ratio of 1:1. Patients with intermediate or poor prognosis were recommended to allogeneic Hematopoietic stem cell transplantation (HSCT) (Allo-HSCT) once achieved first CR. According to NCCN guidelines, patients who refused Allo-HSCT entered three courses of consolidation chemotherapy including at least two courses of high-dose Ara-C (2 g/m 2 q12h) or standard-dose Ara-C combined with an anthracycline. For patients who failed to achieve CR after the initial induction chemotherapy, a standard dosage induction therapy (DA3+7, daunorubicin 45 mg/m 2 , Ara-C 100 mg/m 2 ) was applied.

Efficacy evaluation
Bone marrow was collected between 28 and 35 days from the date of discontinuation of chemotherapy. Bone marrow morphological detection, cytogenetics, and genetic detection were performed to evaluate response. Flow cytometry was performed to evaluate minimal residual disease. Responses were defined as in Ref. [20]: CR as < 5% of bone marrow blasts with normal peripheral blood counts (neutrophils ≥1.0 × 10 9 /L, platelets ≥100 × 10 9 /L); CR with incomplete hematologic recovery (CRi, neutrophils < 1.0 × 10 9 /L, and/or platelets < 100 × 10 9 /L)); partial remission (PR) as bone marrow blasts 5-25%; No response (NR) as bone marrow blast > 25% and a decrease of pretreatment bone marrow blast percentage by less than 50%. ORR was calculated as the sum of CR, CRi, and PR. Neutrophil recovery was defined as days from the course start of induction therapy to neutrophil recovered to > 0.5 × 10 9 /L. Platelet recovery was defined as days from the course start of chemotherapy to platelets recovered to > 20 × 10 9 /L for twice evaluation without platelet transfusion.

Safety evaluation
Toxicity was assessed using National Cancer Institute Common Terminology Criteria for Adverse Events version 5.0 (https://ctep.cancer. gov/protocolDevelopment/electronic_applications/ctc.htm#ctc_50).    Nine patients who did not achieve CR proceeded to a course of traditional induction chemotherapy. Three patients died during the marrow suppression period due to infections or hemorrhage. The remaining six patients still did not achieve CR after the second course and were verified as primary refractory leukemia.

Long-term outcomes
The

Adverse events
The CA regimen was generally safe and had reversible adverse effects.
All patients attained grade IV myelosuppression, but no patients died in the first course of induction chemotherapy ( No cardiac toxicity was reported by the end of follow-up. The incidence of nonhematologic adverse events was similar between the two groups.

DISCUSSION
The regimen of DA(3+7) has long been used as a standard induction chemotherapy for AML patients, and efforts have been made to improve the CR rate by escalating the dosage of daunorubicin.
The CR/CRi rates of induction chemotherapy using daunorubicin 60-90 mg/m 2 for 3 days were 66-68% [10]. Another research reported that the patients who received daunorubicin (50 mg/m 2 daily for 5 days) or idarubicin (12 mg/m 2 for 3 days) achieved a similar CR rate (77.5% vs 78.2%) [16]. In this study, we evaluated the efficacy of an anthracycline-free regimen in treating newly diagnosed adult AML.
Our results demonstrate that the induction regimen of CTX and Ara-C was efficacious for AML patients. With one course of induction, the CA regimen achieved a CR/CRi rate of 80%, similar to that of the DA regimen. Patients who did not respond to CA treatment also did not benefit from DA regimens.
Disease would relapse in nearly all CR patients without proper consolidation treatment [21]. The same results were observed in this study.
Patients who gave up consolidation chemotherapy relapsed and died within a few months, thus led to a poor OS. In patients younger than 60 years who received intense chemotherapy but not followed by Allo-HSCT, the reported 10 years survival and disease-free survival (DFS) was only 16.6%. Patients elder than 60 years showed even worse DFS [22]. Unexpectedly, patients in our study who completed the consolidation chemotherapy showed an expected 5 years OS and RFS reached to 64%, higher than that of traditional treatment [9,10,23]. Hemorrhagic cystitis 0(0) 1 (5) High-dose Ara-C may overcome cytarabine resistance in leukemic blasts and has been used successfully as a salvage regimen for AML as well as in postremission therapy [24]. However, studies showed that using Ara-C at > 1 g/m 2 during induction did not increase efficacy in newly diagnosed AML [25,26], but increased drug toxicity (NTR230) [27]. Therefore, we adopted Ara-C 1 g/m 2 for induction chemotherapy in our study. CTX is an inactive prodrug that requires enzyme and chemical activation. Considering severe adverse events to heart or liver that often occur in HSCT patients using CTX 60 mg/kg for preconditioning, we reduced the dosage to 20 mg/kg per day. The regimen was generally safe, and we did not observe severe nonhematological toxicity. All patients survived using the current dose of Ara-C and CTX, indicating its safety as an induction therapy. Importantly, the CA regimen shortened the chemotherapy duration from traditional 7 days to 4-5 days, which significantly reduced the patients' torture both physically and mentally.
One concern of the hematologic toxicity of the induction regimen is the duration of agranulocytosis that resulted in life-threatening infections. It usually takes 29 ± 10 days for neutrophile to recover to > 0.5 × 10 9 /L in traditional chemotherapy [9,10,23]. The median Absolute Neutrophil Count (ANC) recovery time of the CA regimen was 18 days, with faster recovery in the CA4+3 group. This may attribute to the rapid obliteration of the leukemic cells due to the higher cumulative drug concentration and sustained long-lasting plasma concentration of Ara-C daily used in the CA4+3 group than that in the CA4+5 group.
In this study, we first time demonstrate that the CA regimen could achieve high CR rate and long-term survival in newly diagnosed AML,