Phase II Trials of Clofarabine in Relapsed or Refractory Pediatric Leukemia.

Background: Clofarabine, a next generation nucleoside analogue, was well tolerated and demonstrated activity in adult and pediatric Phase I trials conducted in heavily pretreated leukemia patients. Multicenter Phase II studies in pediatric leukemia have completed accrual in the US and are reported here.

Methods: Two Phase 2, multicenter, open-label studies were conducted with clofarabine in children with refractory or relapsed ALL or AML. Clofarabine was administered intravenously over 2 hours at 52 mg/m²/day for 5 consecutive days. Cycles were repeated every 2 to 6 weeks based on response and toxicity.

Results: The studies enrolled 100 patients (60 ALL and 40 AML). Currently, data are available for 84 patients (49 ALL, 35 AML). Median age is 12 years (range 1 to 22 years) and median number of prior regimens is 3 (range 1 to 6). Thirty-nine percent had received prior bone marrow transplant (BMT). As determined by independent review, preliminary data indicate overall response rates of 31% in ALL (6 CR, 4 CRp, and 5 PR) and 26% in AML (1 CRp and 8 PR). Median duration of remission for ALL is 9.7 weeks (range 1.0 to 28.6) and for AML is 16.2 weeks (range 1.7 to 56.6+). Thirteen of 24 responding patients (54%) proceeded to BMT. Median survival was 42 weeks (range 7.0 to 63.1+) for responding ALL patients (CR+CRp+PR) and 39 weeks (range 7.7 to 93.6+) for responding AML patients (CRp+PR). Patients who failed treatment or were non-evaluable had shorter median survival; 7.4 weeks (range 0.9 to 40.1+) and 12.4 weeks (range 1.6 to 84.9+) for ALL and AML, respectively. Among the patients who were refractory to the last prior chemotherapy, 7/30 (23%) with ALL and 4/22 (18%) with AML achieved a response with clofarabine. Median duration of remission in these patients is 4.6 weeks (range 2.3 to 24.4+) for ALL and 20 weeks (range 1.7 to 56.6+) for AML. Most drug-related adverse events were transient including febrile neutropenia, diarrhea, nausea/vomiting, fever, skin rash, headache, elevation in liver enzymes and bilirubin, and infusion-related flushing and anxiety.

Conclusions: Clofarabine is active as a single agent in pediatric ALL and AML that are refractory to intensive salvage regimens. The overall safety profile is similar to that reported in other pediatric salvage studies. Clofarabine in combination with standard chemotherapy is currently under investigation in children.