Analyzing the Effects of Obesity and Ethnicity on Outcomes of Pediatric Patients with Hematologic Malignancies Receiving Haploidentical Stem Cell Transplant with Post-Transplant Cyclophosphamide (PTCy): A Single Center Experience

Hematopoietic stem cell transplant (HSCT) is a curative treatment option for many pediatric patients with high-risk hematologic malignancies. A matched sibling donor is recognized as the preferred donor source, however is not available for the majority of patients. Additionally, a fully matched unrelated donor is more difficult to find for underrepresented ethnic minorities. The advantage of prompt identification and availability of a suitable donor, while also taking steps to prevent graft versus host disease (GVHD) has led to the use of haploidentical donors (haplo) with post-transplant cyclophosphamide (PTCy). Studies have examined the use of PTCy with different types of conditioning regimens and diagnoses; however, there is little data examining the effects of obesity and ethnicity on outcomes for pediatric patients. For this reason, we performed a retrospective review of fifty pediatric patients with hematologic malignancies treated with haplo-HSCT using PTCy at Texas Children's Hospital from 2017-2023. The median age at transplant was 14.5 years (range: 0.7-21.1 years). The majority received transplants for acute leukemia (54% ALL (n=27) and 34% AML (n=17)), while 68% (N=34) were Hispanic and 24% (N=12) met diagnostic criteria for obesity. The 1-year overall survival (OS) for the entire cohort was 72% (95% CI:57-83%), with a 1-yr disease free survival (DFS) of 69% (95% CI:53-81%), cumulative incidence of relapse (CIR) of 23%, and non-relapse mortality (NRM) of 19%. The incidence of aGVHD grade III-IV and extensive cGvHD was 11% and 14%, respectively. When comparing ethnic groups, Hispanic and non-Hispanic patients have comparable 1-yr OS and DFS (75% v 67% and 71% v 65%, respectively). Obese patients had a lower 1-yr OS compared to non-obese patients, though this was not significant (51% v 78%, p=0.167), and did have a significantly worse 1-yr DFS (44% v 77%, p=0.030), likely related to a significantly increased CIR (44% v 15%, p=0.016). Hispanic patients and obese patients had comparable NRM, incidence of grade III-IV aGVHD and incidence of extensive cGVHD to their non-Hispanic and non-obese counterparts. These findings represent one of the largest single center cohorts utilizing haplo-HSCT with PTCy in a pediatric hematologic malignancy population. Low rates of NRM and acute and chronic GVHD suggest that this is a safe and well-tolerated approach even in the setting of an underrepresented population. Additionally, non-inferior outcomes for Hispanic patients highlights the fact that haploidentical donors are a good option for a population who may not have suitable matches available in the national registry. Finally, interestingly the increased CIR and inferior DFS in our obese patient population could be secondary to chemotherapy dose adjustments, which requires further analysis.