NPM::ALK Transcript Levels and Anti-ALK Autoantibody Titers As Biomarkers for Outcome in Pediatric ALK+ Anaplastic Large Cell Lymphoma Treated with Brentuximab Vedotin or Crizotinib in Combination with Chemotherapy: COG ANHL12P1

Anaplastic Large Cell Lymphoma (ALCL) is a CD30+ T-cell lymphoma accounting for ~10% of pediatric non-Hodgkin Lymphoma which is often driven by fusions resulting from translocations involving the anaplastic lymphoma kinase (ALK) and nucleophosmin (NPM1) genes. The COG-sponsored ANHL12P1 trial assessed brentuximab vedotin (BV) or crizotinib (CZ) combined with standard chemotherapy in newly diagnosed pediatric ALK+ALCL. It has previously been reported that levels of NPM::ALK fusion transcript and immune response to the NPM::ALK antigen, as determined by ALK autoantibody (Ab) titers, are predictive of outcomes, but the significance of these biomarkers following either BV or CZ is unknown. Methods: Patients <22 years of age with newly diagnosed ALCL were randomly assigned to receive BV or CZ in combination with an ALCL-99 chemotherapy backbone. Serial assessments for NPM::ALK fusion transcript and Ab to ALK were performed using peripheral blood samples. NPM::ALK transcript levels were measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and normalized to the copy numbers (NCN) per 10⁴ copies of the ABL gene. Based on prior studies >10 NCNs were considered a positive result and an ALK Ab titer of >1:750 was classified as a high-titer. Results: In total, 137 patients were enrolled with 68 and 69 patients randomized to the BV and CZ arms, respectively. Minimal residual disease (MRD), defined as detectable NPM::ALK transcript post-cycle 1, was associated with an inferior 2-year EFS overall (20.0% vs. 85.8% MRD-; p<0.0001), and by treatment arm (BV: 28.6 vs 91.1%, p<0.0001; CZ: 81.4 vs. 0.0%, p<0.0001). The evolution of transcript levels from baseline (minimal detectable disease, MDD) to post-cycle 1 (MRD) enabled the stratification of patients into three risk groups based on their associated 2-year EFS: low (MDD-/MRD-): 92.2%, and high (MDD+/MRD+): 12.5% (p<0.0001). High vs. low anti-ALK Ab titers at baseline did not impact EFS overall (80.8% vs. 73.9%, p=0.15) or by treatment arm (BV: 79.3% vs. 81.0%, p=1.0; CZ: 82.4% vs. 68.7%, p=0.08). Titers post-cycle 1 were not associated with outcome in the CZ arm (EFS 82.6% vs 74.2% for high-titer vs low-titer, p=0.42), but high-titer in the BV arm and in the entire population overall resulted in superior 2-year EFS of 89.9% vs. 68.0% (p=0.03) and 86.7% vs. 71.6% (p=0.04) respectively. Persistence of a high-titer from baseline through post-cycle 1 resulted in a superior 2-year EFS of 88.2%, compared to 73.1% and 68.4% for patients with persistent low titers and those transitioning from high to low-titers, respectively (p=0.01). Conclusion: In this study of pediatric ALK+ ALCL, NPM::ALK transcript levels proved to be a critical prognostic marker, with detectable MRD significantly associated with poor outcomes. Conversely, following the initiation of treatment the presence and persistence of high anti-ALK Ab titers showed promise as a favorable prognostic marker. These findings underscore the importance of serial monitoring of NPM::ALK transcript levels and anti-ALK Ab titers in guiding therapeutic strategies and predicting outcomes in pediatric ALK+ ALCL. Further studies are warranted to validate these biomarkers and explore their potential for personalized treatment approaches.