Pediatric-Inspired Chemotherapy Incorporating Pegaspargase Is Safe and Results in High Rates of MRD Negativity in Adults Ages 18-60 with Philadelphia Chromosome-Negative Acute Lymphoblastic Leukemia and Lymphoblastic Lymphoma

Introduction: Among adolescents and young adults with (w/) acute lymphoblastic leukemia (ALL) or lymphoblastic lymphoma (LBL), treatment using a pediatric (vs. adult) regimen appears to achieve superior event-free (EFS) and overall survival (OS); this observation has driven increased interest in adapting pediatric regimens for middle-aged adults w/ ALL/LBL. However, greater risk of toxicities associated w/ asparaginase complicates administration of pediatric-inspired regimens in adults. We therefore designed a pediatric-inspired chemotherapy regimen w/ doses of pegaspargase (PEG) rationally synchronized to limit overlapping toxicities w/ other chemotherapeutic agents.

Methods: We conducted a phase II multi-center trial in adults ages 18-60 w/ newly-diagnosed Philadelphia chromosome-negative (Ph-) ALL/LBL (NCT01920737). Pts w/ Ph+ ALL or Burkitt-type ALL were ineligible. The treatment regimen consisted of 2-phase induction (I-1, I-2), followed by consolidation w/ 2 courses of alternating high-dose methotrexate-based intensification and reinduction, followed by 3 years of maintenance (Figure 1). PEG 2000 IU/m² was administered in each of the 6 intensive courses of induction/consolidation at intervals of ≥4 weeks. Minimal residual disease (MRD) was assessed in bone marrow (BM) by multiparameter flow cytometry (FACS) on day (d) 15 of I1 and following I-1 and I-2. Any detectable MRD (even <0.01% of BM WBCs) was considered positive. Toxicities were assessed by CTCAE v4.0.

Results: 39 pts were enrolled (30M, 9F), w/ B-ALL (n=28), T-ALL (n=7), B-LBL (n=3), and T-LBL (n=5). Median age at start of treatment was 38.3 years (range 20.2-60.4), w/ 18 pts age 40-60.

Grade 3-4 toxicities associated w/ PEG are summarized in Table 1. Grade 3-4 hyperbilirubinemia was observed post-PEG in I-1 in 9 pts, but only recurred thereafter in 1/8 pts resuming PEG. Pts completing consolidation on protocol (n=16) received median of 6 doses of PEG (range, 2-6). Four pts developed hypersensitivity to PEG and subsequently received Erwinia asparaginase. PEG was discontinued in 4 additional pts due to hepatotoxicity (n=2), pancreatitis (n=1), and physician preference (n=1).

Of pts w/ available response assessments, 35/36 (97%) achieved morphologic complete response (CR) or CR w/ incomplete hematologic recovery (CRi) following I-1 (n=34) or I-2 (n=1). Both pts not achieving CR/CRi after I-I had early T-precursor ALL; one of these pts was withdrawn from study, and the other (w/ M2 marrow after I-1) achieved CR after I-2.

Of the pts w/ ALL (excluding LBL) w/ available BM MRD assessments, 11/28 (39%) achieved undetectable MRD by FACS following I-1; 18/22 (82%) achieved undetectable MRD by FACS following I-2. Of the pts w/ LBL w/ available BM MRD assessments, 7/7 (100%) achieved or maintained undetectable MRD by FACS following I-1 and I-2. Ten pts underwent allogeneic hematopoietic cell transplantation (alloHCT) in CR1. Seven pts experienced relapse at median 15.2 months from start of treatment (range, 5.4-30.4), of whom 6 subsequently underwent 1^st (n=5) or 2^nd (n=1) alloHCT. Of the 11 pts w/ ALL w/ undetectable MRD following I-1, only one has relapsed. Five patients have died, including 2 pts in CR1 (from sepsis and multi-organ system failure), and 3 pts in relapse.

At median follow-up of 22.3 months among surviving pts (range, 1.0-48.1), median EFS and OS (Figure 2A&B) have not been reached (EFS not censored at alloHCT). 3-year EFS was 62.1% (95% CI: 38.4-78.9%) and 3-year OS was 80.0% (95% CI: 57.5-91.4%).

Conclusions: PEG can be incorporated into pediatric-inspired chemotherapy regimens w/ manageable toxicity for appropriately selected adults up to age 60 w/ Ph- ALL/LBL. While PEG-related AEs are common, few pts require permanent discontinuation of asparaginase. Grade 3-4 hyperbilirubinemia was common, particularly post-I-1, but recurred infrequently when PEG was continued. Two induction courses resulted in a high rate of MRD negativity post-I-2 and translated to a low rate of relapse. Though further follow-up is required, 3-year EFS is encouraging. Data regarding asparaginase enzyme activity and silent inactivation w/ neutralizing anti-PEG antibody will be presented. Ongoing and future studies will additionally investigate whether incorporating novel therapies (e.g. blinatumomab, nelarabine) into frontline consolidation therapy may reduce risk of relapse among adults receiving PEG-containing regimens.

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