Prognostic factors for survival after relapsed acute lymphoblastic leukemia (ALL): A Children’s Oncology Group (COG) study.

10008 Background: Survival of pediatric ALL patients (pts) now approaches 90%, but is historically poor for those who relapse. Methods: In the largest cohort assembled to date we analyzed overall survival (OS) rate post relapse, defined as duration between date of relapse and death, among pts diagnosed from 1996-2014 treated on 10 contemporary COG frontline trials. Comparisons of post-relapse OS were based on logrank tests, with two-sided p values reported. Results: Of 15,874 pts enrolled on frontline trials, 1,967(12%) relapsed. Relapse rates ranged from 35% in infant ALL to 9.7% in pts with NCI standard risk B-ALL. Rates were similar for T and B-ALL, 11% vs. 12%. Relapse patterns differed by phenotype: almost half of non-infant B-ALL relapses occurred late (≥36 mos), and at all time periods bone marrow (BM) relapse predominated. Conversely 65% of T-ALL relapses were early ( < 18 mos) with similar number of isolated CNS (iCNS) and isolated BM (iBM) relapses. Median time to relapse was shorter for infant ALL and T-ALL (both 13.8 mos) compared to B-ALL (34.4 mos). The 5yr OS rates (±SE) after relapse for B, T, and infant ALL were 52±1%, 33±3% and 19±4%, respectively, with greater variability in OS by site in T vs. B-ALL. 5yr OS rates for pts with early BM relapse was similar for both B and T-ALL (28%), but pts with B-ALL who relapsed between 18-36 mos fared better than pts with T-ALL (OS 50±2% vs 34±8%, p = 0.014). The 5yr OS rates for pts with late relapses were 65±2% for B-ALL and 50±12% for T-ALL. In multivariable analysis, time to relapse, site of relapse, age < 1 or > 10 yrs at diagnosis, initial WBC > 100K, and T-cell phenotype were associated with worse outcomes post relapse (all p < 0.01). Sex, CNS status at diagnosis, or prior therapy on POG versus CCG/COG backbone did not influence OS. Compared to pts treated from 1988-2002 (Nguyen et al. Leukemia 2008), 5yr OS rate post relapse has improved over time for B-ALL from 37±2% to 52±1% (p < 0.001) and T-ALL from 23±4% to 33±3% (p < 0.05). 5-yr OS rates improved significantly for pts with iBM from 24±2% to 45±2% (p < 0.001) and marginally for pts with iCNS from 59±3% to 65±3% (p = 0.15). Conclusions: In the modern era there are fewer relapses for B and T-ALL, however sites of recurrence and outcomes differ by phenotype. Infants continue to do poorly. Compared to prior analyses, survival after relapse is significantly improved.