Bortezomib reinduction therapy to improve response rates in pediatric ALL in first relapse: A Children's Oncology Group (COG) study (AALL07P1)

Background: Bortezomib (bortez) is a reversible inhibitor of the 26S proteasome. Promising results have been reported adding bortezomib to reinduction chemotherapy in patients (pts) with ALL in 2nd or later relapse (Messinger, Blood 2012). Methods: This was a phase 2 study of bortez with reinduction chemotherapy in 1st relapse pediatric ALL that enrolled pts with pre-B ALL (relapse <36 months (m) from diagnosis). This report summarizes results from 61 evaluable pre-B ALL pts 21 yrs old, either <18m (stratum 1) or 18-36m (stratum 2) from diagnosis. Therapy consisted of bortez (1.3 mg/m2, days 1, 4, 8, and 11) with reinduction chemotherapy (vincristine, prednisone, PEG-asparaginase, doxorubicin). Complete response (CR2) rates and minimal residual disease (MRD) were determined at the end of the first 5-week therapy block. AALL07P1 utilized a stratified 2-stage design (London 2005) with the primary objective of comparing CR2 rates at the end of block 1 of therapy to historical control CR2 rates (AALL01P2). Block 2 included cyclophosphamide, etoposide, and bortez followed by 5g/m2 methotrexate. Biology studies included assessment of NF-B activity. Results: 61 evaluable pre-B ALL pts were assessed. Toxicities were similar to AALL01P2, including 10 Grade 3- 4 hypotension, 4 Grade 4 hypertriglyceridemia, 3 Grade 3-4 typhlitis, and 2 Grade 3-4 enterocolitis. There were 2 deaths due to infection. Although Grade 3-4 infections were not infrequent (13 in block 1 and 7 in block 2) there were no reports of respiratory distress syndrome or Grade 4 peripheral neuropathy. 42 of the 61 patients enrolled (18/28 (64%) in Stratum 1 and 24/33 (73%) in stratum 2) attained CR2 at the end of Induction I. Based on CR2 response rate compared to historical controls, the study met its primary response objective. The number of pts in CR2 with MRD <0.1% also improved from AALL01P2; among pts achieving CR2, MRD was <0.1% in 41% (16/39) in AALL01P2 vs. 71% (25/35) (p= 0.073, Fisher's exact test). Conclusions: Based on response rates in the very early and early first relapse pre-B ALL, AALL07P1 met its predefined efficacy benchmark. We conclude that bortezomib is worthy of further study in pediatric ALL.