Clinical Significance of Isolated Myeloperoxidase Expression in Pediatric B-Lymphoblastic Leukemia.
Diagnosis of B-cell acute lymphoblastic leukemia (B-ALL) requires immunophenotypic evidence of B-lineage and absence of specific myeloid or T-lineage markers. Rare cases of otherwise typical B-ALL express myeloperoxidase (MPO) detectable by flow cytometry with an absence of other myeloid markers, but the clinical significance of this finding is not well studied.



A retrospective cohort analysis of flow cytometry and clinical data was performed to investigate the clinical outcome of this specific group of patients.



Twenty-nine cases of otherwise typical B-ALL that expressed MPO by flow cytometry (B-ALL-isoMPO) without expression of other myeloid markers were identified. The B-ALL-isoMPO group had a significantly increased incidence of relapse (univariate log rank P  = .0083; multivariate hazard ratio, 2.50; 95% confidence interval, 1.07-5.85; P  = .034) and significantly worse event-free survival by univariate analysis (log rank P  = .0066) compared with a reference group of patients with B-ALL from the same time period (n = 264).



To our knowledge, this is the first report to document the clinical outcomes in a group of pediatric patients with B-ALL that expresses MPO in the absence of other myeloid markers. This group had an increased rate of relapse and a worse event-free survival than the patients with B-ALL who did not express MPO.
Department of Pathology and Laboratory Medicine, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, 4650 Sunset Blvd., Los Angeles, CA|Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles.
Matthew J
MJ
Oberley
Zhejiang University School of Medicine, Children's Hospital, Hangzhou, China.
Sisi
S
Li
Children's Center for Cancer and Blood Diseases, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California,  Los Angeles, CA
Etan
E
Orgel
Children's Center for Cancer and Blood Diseases Biostatistics Core, Children's Hospital Los Angeles, Los Angeles, CA.
Choo
C
Phei Wee
Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles.
Ashley
A
Hagiya
Department of Pathology and Laboratory Medicine, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, 4650 Sunset Blvd., Los Angeles, CA|Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles.
Maurice R G
MRG
O'Gorman
D000293:Adolescent; D001402:B-Lymphocytes / Q000378:metabolism; D014408:Biomarkers, Tumor / Q000378:metabolism*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D018572:Disease-Free Survival; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D016130:Immunophenotyping; D007223:Infant; D007527:Isoenzymes / Q000378:metabolism; D053208:Kaplan-Meier Estimate; D015448:Leukemia, B-Cell / Q000175:diagnosis* / Q000378:metabolism; D008297:Male; D009195:Peroxidase / Q000378:metabolism*; D012008:Recurrence; D012189:Retrospective Studies; D012306:Risk
D014408:Biomarkers, Tumor; D007527:Isoenzymes; D009195:Peroxidase
B-ALL; Mixed-phenotype acute leukemia; Myeloperoxidase