Impact of Race/Ethnicity on Pediatric Core Binding Factor AML Outcomes and Response to Gemtuzumab Ozogamicin
Authors: Conneely Shannon E. , McAtee Casey L. , Rau Rachel E. 
Published: November 2020

Introduction: Racial disparities in pediatric acute myeloid leukemia (AML) outcomes have consistently demonstrated inferior event-free survival (EFS) and overall survival (OS) in minority populations with the worst outcomes in Black children. However, AML is a heterogenous disease classified by recurrent genetic aberrations, and these disparities have not been thoroughly investigated within specific cytogenetic groups. In addition, race-based response to individual chemotherapy agents in AML has not been explored. Here, we use data from the Therapeutically Applicable Research to Generate Effective Treatments (TARGET) database to describe the effects of race on outcomes and response to gemtuzumab ozogamicin (GO) therapy in core binding factor (CBF) AML, a favorable risk AML subtype.
Methods: CBF AML patient data was extracted from the online TARGET database. Race and ethnicity were self-reported. Estimates of 2-year OS and EFS were calculated using the Kaplan-Meier method and analyzed via log-rank statistic. Pearson's Chi-squared test and Fisher's exact test were used to analyze patient variables.
Results: The OS in CBF AML differed significantly based on race/ethnicity at 87% (95% CI, 82-93%) for White non-Hispanic (WNH), 77% (95% CI, 67-89%) for Hispanic, and 71% (95% CI, 58-88%) for Black children (p=0.005). EFS was also significantly lower in Black (46%; 95% CI, 32-66%) compared to non-Black children (66%; 95% CI, 60-73%)(p=0.023).
When assessed by CBF AML subtype, EFS and OS in t(8;21) AML varied significantly based on ethnicity at 50% (95% CI, 34-75%) and 67% (95% CI, 50-88%) in Black patients, 63% (95% CI, 49-82%) and 69% (95% CI, 55-87%) in Hispanic patients, and 82% (95% CI, 72-92%)(p=0.01) and 90% (95% CI, 93-98%)(p=0.006) in WNH patients. In inv(16) AML, Hispanic patients experienced the highest EFS (71%; 95% CI, 55-92%) followed by WNH (54%; 95% CI, 43-66%) and Black (36%; 95% CI, 17-79%) patients though this did not reach statistical significance (p=0.12). There was no impact of race/ethnicity on OS in inv(16) AML.
The use of GO did not alter OS in any subset of CBF AML. EFS appeared to be slightly improved but was not statistically significant. However, Black children with any type of CBF AML had preferential improvement with GO with significantly higher EFS (69% v. 26%, p=0.03) and a trend toward improved OS (81% v. 63%, p=0.19) with GO therapy. These improvements were primarily driven by a significant increase in EFS in inv(16) AML when treated with GO (80% v. 50%, p=0.01) and a similar but non-significant improvement in OS in this group. In Hispanic children there was a trend toward inferior EFS with the use of GO (63% v. 73%, p=0.37) in CBF AML, particularly in t(8;21) patients with a 1-year EFS of 56% (95% CI, 37-87%) compared to 81% (95% CI, 64-100%)(p=0.23).
WNH children were more likely to achieve Complete Remission (CR) after course 1 (OR 2.36, 95% CI 1.09-5.10, p=0.03), and Black children were more likely to have persistent Minimal Residual Disease (MRD) after course 2 (OR 9.64, 95% CI 2.48-37.43, p&lt;0.001). No differences were detected in other patient variables.
Conclusion: Children with CBF AML represent a favorable cytogenetic risk group with an EFS of 70% and OS of 85%. However, the impact of race/ethnicity on outcome is significant with Black children experiencing the lowest EFS and OS at 46% and 71%, respectively, with this trend persisting across cytogenetic subtypes. Black children were also more likely to remain MRD positive after Induction II and less likely than WNH patients to achieve CR. However, while the addition of GO to standard therapy did not improve outcomes in CBF AML overall, Black children selectively benefited from GO therapy. Black children trended toward improved EFS and OS with GO with the most pronounced effect on EFS in inv(16) which was improved from 50% to 80% at 1 year. These results demonstrate that Black children with CBF AML are disproportionately at risk for poor outcomes compared to other ethnicities, but these risks may be mitigated by the use of GO which increase EFS and OS primarily in this group. Conversely, Hispanic patients trended toward worse EFS with GO, particularly in t(8;21) AML, possibly due to treatment-related toxicity. As CD33 expression and certain ABCB1 SNPs are known to predict response to GO therapy, our ongoing work investigates racial differences in these variables as a potential explanation for the differing responses to GO.

Disclosures
Rau: Jazz Pharmaceuticals, Inc.: Consultancy, Other: Travel Fees.