# Persistent BCR::ABL1 p190 Minimal Residual Disease and Declining Donor Chimerism Following Haploidentical Bone Marrow Transplant in Pediatric Acute Myeloid Leukemia With Dual High-Risk Fusions

## TL;DR

A child with a rare and high-risk form of leukemia had persistent cancer cells after a bone marrow transplant, highlighting the difficulty in eliminating all cancer cells in such cases.

## Contribution

This case study highlights the persistence of BCR::ABL1 p190 MRD and declining donor chimerism in a high-risk pediatric AML patient post-haploidentical transplant.

## Key findings

- Persistent BCR::ABL1 p190 expression was detected despite hematologic recovery after transplant.
- Donor chimerism declined from 100% to 86% by day +180, with CD3-positive donor cells at 72%.
- The case emphasizes the challenge of eradicating leukemic stem cells in high-risk AML.

## Abstract

We recently reported a de novo acute myeloid leukemia (AML) patient harboring both BCR::ABL1 p190 isoform and RUNX1::MECOM fusion, a rare and high-risk molecular profile. In this follow-up, we present the patient’s post-transplant course with serial minimal residual disease (MRD) monitoring. MRD was tracked via quantitative polymerase chain reaction (qPCR) for the p190 isoform, and chimerism was assessed using short tandem repeat-polymerase chain reaction with capillary electrophoresis. The patient underwent haploidentical bone marrow transplantation after standard induction therapy complicated by sepsis and myocarditis. Post-transplant recovery was marked by poor initial engraftment, requiring platelet transfusions and biweekly filgrastim. A CD34+ boost on day +63 improved platelet counts and eliminated transfusion dependence by day +103. Chimerism studies showed a decline in donor DNA from 100% on days +30 and +60 to 86% by day +180, with CD3-positive donor cells at 72% on day +189. Despite hematologic recovery, qPCR consistently revealed persistent BCR::ABL1 p190 expression, indicating residual disease. This case underscores the challenge of eradicating leukemic stem cells (LSCs) in high-risk AML and supports the integration of next-generation flow cytometry for enhanced MRD and LSC assessment post-transplant.