Background KMT2A-rearranged acute lymphoblastic leukemia (KMT2A-r ALL) is a rare and dismal disease in infants. Despite restriction of the indication of allogeneic hematopoietic stem cell transplantation to the high-risk group (patients aged <180 days with KMT2A-r ALL or central nervous system involvement), adoption of an Interfant-06-based induction therapy with stricter age-related dosing followed by COG AALL0631-based post-remission chemotherapy with additional administration of high-dose cytarabine in the early intensification phase led to rapid clearance of minimal residual disease (MRD) in the Japanese Pediatric Leukemia/Lymphoma Study Group (JPLSG) MLL-10 trial. The MLL-10 trial demonstrated an improved outcome of 66.2% in 3-year event-free survival (EFS) among infants with KMT2A-r ALL (Tomizawa D. Blood 2021). As the Interfant-06 study showed an association between the expression levels of myeloid markers (MM) and poor MRD clearance at end of induction (EOI) and a high relapse rate (Stutterheim J, J Clin Oncol.2021), we analyzed the significance of MM expression in the MLL-10 cohort and its association with prognosis.

Methods

We analyzed and compared the MM expression (defined as at least one positive marker [with a positive blast subset ≥ 10%] among CD117, CD13, CD33, and CD65/CD15) by using flow cytometry (FCM) in infants with KMT2A-r ALL who were registered in the JPLSG MLL-10 trial. We also compared the results of immunoglobulin/T-cell receptor (Ig/TCR) gene-based polymerase chain reaction (PCR)-MRD analyses or 4-color FCM-MRD assay between the MM-positive and MM-negative groups at EOI and end of early consolidation. The Ig/TCR-MRD results were classified as negative if <5 × 10 −4 and positive if ≥5 × 10 −4, while the FCM-MRD results were classified as negative if <0.01% and positive if ≥0.01%. We prioritized PCR-MRD and used FCM-MRD when we could not make a primer for PCR-MRD. The presence of MRD was not used as a basis for choosing the appropriate therapy.

Results and Discussion

Among the patients with KMT2A-rALL, 74 were included in this study, excluding one who was not evaluated with FCM at diagnosis. Of these patients, 42 were MM-positive and 32 were MM-negative. The 3-year EFS rates of the MM-positive and MM-negative patients were 62.3% (95% confidence interval [CI], 45.5-75.3) and 70.0% (95% CI, 50.3-83.1), respectively (p = 0.61). Their 3-year overall survival rates were 80.6% (95% CI, 65.0-89.8) and 87.5% (95% CI, 70.0-95.1), respectively (p = 0.74). The numbers of MM-positive and MM-negative patients according to age group are summarized in Table 1, and the difference in age distribution between the two groups was not significant. The MRD statuses of the patients at EOI in the two groups are also summarized in Table 1. No significant difference in MRD clearance was found between the MM-positive and MM-negative groups.

Conclusion

In this study, we found no significant difference in survival rate between the MM-positive and MM-negative groups. The MM expression was not a prognostic marker in the infants with KMT2A-r ALL in the MLL-10 cohort. We believe that rapid MRD clearance in the early phase of treatment with enhanced chemotherapy would have the greatest contribution to the improvement of prognosis. In this study, the MM-positive patients from the MLL-10 cohort might have benefited from early-phase treatment intensification in terms of MRD clearance.

Figure 1
Figure 1.
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Disclosures

No relevant conflicts of interest to declare.

© 2021 by The American Society of Hematology
2021
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