Clofarabine with Topotecan, Vinorelbine, and Thiotepa (TVTC) in Children and Young Adults with Relapsed or Refractory Acute Myeloid Leukemia

Background: Relapsed or refractory pediatric acute myeloid leukemia (AML) is an unfortunate reality in approximately 40% of children and young adults diagnosed with AML. Therapeutic options are limited in this heavily pre-treated patient population, many of whom have reached lifetime recommended doses of anthracycline chemotherapy. Non-anthracycline based salvage regimens are crucial to these patients who are at significant risk of life-threatening cardiotoxicity. We previously reported results of a phase 2 trial of a Clofarabine-based regimen with Topotecan, Vinorelbine, and Thiotepa (TVTC) in a cohort of patients with AML. Herein, we report on an expanded cohort of AML patients treated at Memorial Sloan Kettering Cancer Center (MSKCC) since 2007. We report our center's experience using a Clofarabine-based regimen with Topotecan, Vinorelbine, and Thiotepa (TVTC), its overall response rate defined as complete remission (CR) and its use as a bridge to hematopoietic stem cell transplant (HSCT).

Patients and Methods: All patients <25 years of age with relapsed/refractory AML, defined as >10% bone marrow involvement, who were treated with the phase 2 recommended schedule of TVTC were included in this analysis. Patients received the TVTC regimen with Topotecan 1 mg/m2/day (120 hour continuous infusion, Days 0-4), Vinorelbine 20 mg/m2/dose (Days 0, 7, 14), Thiotepa 15 mg/m2/dose (Day 2), and Clofarabine 40 mg/m2/day (Days 3-7). The regimen could be administered without hospitalization in patients who did not require hospitalization for other reasons. Most patients received antimicrobial prophylaxis starting on Day 8 with Levofloxacin and fungal prophylaxis with either Posaconazole or Voriconazole. GCSF 5mcg/kg/day was initiated on Day 8. Bone marrow evaluation was performed at the point of hematologic recovery to assess response. Overall response rate (ORR) was defined as complete remission (CR) plus complete remission without platelet recovery (CRp).

Results: A total of 29 patients with relapsed (n=19) or refractory (n=10) AML were treated since 2007. Eight patients (28%) had prior hematopoietic stem cell transplantation (HSCT). The ORR of the entire cohort was 59% (17/29). The ORR of patients with relapsed vs. refractory disease was 74% (14/19) and 30% (3/10), respectively. Seventeen of 29 patients (59%) received TVTC as a 1^st re-induction regimen with 59% (10/17) of those patients achieving a CR/CRp. The remaining 12 patients had TVTC as 2^nd or greater regimen with 58% (7/12) of those patients achieving a CR/CRp. Among the 17 total responders in the cohort, 13 (76%) proceeded to HSCT. Of those who proceeded to HSCT, 8 of 13 are alive today (62%). Median time since HSCT is 66 months (range 14 to 107 months). The most common adverse effects were febrile neutropenia in 20 out of 29 patients (69%) which was Grade 3 or less, 3 of 29 patients (10%) with Grade 4 or greater febrile neutropenia requiring ICU admission. One patient developed an abdominal mucormycosis infection. One patient developed bone marrow aplasia and died due to sepsis 45 days after receiving TVTC.

Conclusions: TVTC is an active regimen for children and young adults with relapsed/refractory AML, with an acceptable toxicity profile . Non-anthracycline containing salvage regimens are especially important as patients usually receive >400mg/m2 daunorubicin equivalents during frontline therapy. The majority of responders were successfully bridged to HSCT without exposure to additional anthracycline, with approximately half of these patients demonstrating long-term survival. TVTC warrants further exploration as a re-induction regimen in a larger cohort of patients with relapsed/refractory AML.