Updated outcomes for patients with completely resected pulmonary recurrent osteosarcoma: A report from the Children’s Oncology Group

10023 Background: Amongst patients with recurrent osteosarcoma (OS), those with resectable pulmonary-only relapse appear to have the best outcomes. Prior analysis of patients with completely resected recurrent OS enrolled on a Children’s Oncology Group (COG) Phase 2 trial AOST0221, which studied the efficacy of inhaled GMCSF, showed a 12- month disease control rate (DCR12) of only 20% (95% CI, 10 – 34%). DCR12 based on this analysis was used as the historical benchmark for efficacy analysis in two recently completed trials, AOST1321 (completely resected cohort only) and AOST1421. We analyzed the stability of the DCR12 benchmark using data from these contemporary studies. Methods: Patients were eligible for AOST1321 if they had undergone resection of all sites of recurrent or refractory OS within 30 days of enrollment and for AOST1421 if they had lung only recurrent OS completely resected within 4 weeks of enrollment. AOST1321 evaluated denosumab while AOST1421 evaluated dinutuximab. Patients with refractory disease, extrapulmonary recurrence or without histological confirmation of relapse were excluded from this analysis. DCR12 was defined as having at least stable disease 12 months after the start of protocol therapy. We report the DCR12 observed on AOST1321, AOST1421 and AOST0221. Results: One hundred and twenty-eight evaluable patients with completely resected recurrent OS were enrolled on AOST0221 (N=49), AOST1321 (N=38) and AOST1421 (N=41). One hundred and one patients were included in this analysis (AOST0221: 37, AOST 1321: 25, AOST1421:39). DCR12 was 14 % (95% CI, 5% – 26%) for AOST0221, 24% (95%CI 10-42%) for AOST1321, and 31% (95% CI, 17% - 45%) for AOST1421. Risk for disease progression did not differ across the 3 included studies. DCR12 for all three studies combined was 23% (95% CI, 15% – 31%). Conclusions: Prognosis for recurrent OS remains dismal, even for those with resectable pulmonary-only disease. Although not statistically significant, dinutuximab may have activity in a select group of relapsed OS patients; combination studies using dinutuximab are planned. The previously described benchmark of disease control at 12 months remained relatively consistent in recent studies for those patients who have resectable pulmonary-only relapse. Therefore, DCR12 remains a useful outcome measure in fully resected OS with lung only metastases. Analyses are ongoing to better define the appropriate threshold to define investigational agent activity in this specific patient population.