Isolated Myeloperoxidase Immunohistochemical Expression in Bone Marrow Biopsy Depicts Clinical Outcomes in Adults with Typical B-Acute Lymphoblastic Leukemia.

Introduction: Recently, isolated myeloperoxidase expression (isoMPO) has been documented in B-acute lymphoblastic leukemia (B-ALL) and several contradictory studies addressed its clinical significance in pediatric patients.

Aim: In this study, isoMPO was evaluated in bone marrow biopsies (BMB) from adults with B-ALL using immunohistochemistry (IHC) in relation to a number of risk-stratification factors and patients' outcomes.

Methods: Sixty B-ALL adult patients were selected upon electronic database search. Demographic, clinical, laboratory, therapy and survival data were reviewed and tabulated. Flowcytometry (FCM), histopathology and IHC available material were reviewed to confirm the diagnostic criteria according to our standard laboratory protocols. IHC was performed on BMB using antiMPO. Cases were divided into MPO+ve and MPO-ve based on a 3% blast cell staining threshold.

Results: Using IHC, 26.7% of B-ALLs were MPO+ve, in most of which ≥10% of blasts were stained. Among standard risk-stratification factors, isoMPO was associated with a mean WBC count above 30x109/L. MPO+ patients achieved therapeutic complete remission at lower rates and were more prone to progressive/refractory disease and relapse. There was a concordant expression of MPO in FCM and IHC. All of the aforementioned parameters reached the level of significance when compared to the MOP-ve group. Kaplan-Meier curves revealed a significantly lower survival probability for the MPO+ group than the MOP-ve one (p= 0.0066; Log-rank test) and also when separating MPO+ and -ve patients by gender (p= 0.0033; Log-rank test).

Conclusion: isoMPO occur in a considerable percentage of B-ALL in adults contributing to misdiagnosis. It depicts poor outcomes and might be introduced as a B-ALL risk-stratification factor.
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