Abstract
Abstract 3525
The Fcγ receptor I alpha chain (CD64) is usually used as a monocytic marker in immunophenotyping acute myeloid leukemia (AML). The clinical relevance of CD64 expression is controversial and has been reported to be associated with good outcome in the adult population in one large study. The prognostic relevance of CD64 in pediatric AML is not known. More importantly, the outcome is not known when patients expressing CD64 on the surface of their blasts are considered for allogeneic hematpoietic stem cell transplantation (HSCT). We investigated whether HSCT can neutralize the adverse effects of CD64 expression in pediatric AML patients.
Immunophenotype data of 53 pediatric patients with AML, all treated with allogeneic HSCT, was reviewed. The expression of the CD64 on the blast population as determined by flow cytometry was correlated with clinical data and outcome. The median age of patients was 8 years (range: 8 months–14 years) and included 40 (75%) patients transplanted in first complete remission (CR1). Thirty eight (72%) of all patients had intermediate-risk cytogenetics and the remaining (28%) had adverse-risk cytogenetic abnormalities. Only 6 of the 53 patients (11%) had MLL rearrangement as determined by karyotyping and FISH studies.
Fifteen (28%) of all studied patients expressed CD64 on the surface of the blasts at diagnosis. Patients with CD64 expression had significantly shorter overall survival (P=0.005) with median survival of approximately 9 months while the median survival in the CD64 negative patients has not been reached. Similarly, CD64 positive patients had significantly shorter event free survival (EFS) (P=0.004). Even when we considered only patients treated with in CR1 who had HSCT, the OS and EFS for the CD64 positive patients were both significantly shorter (P=0.01 and P=0.009, respectively). The median survival was 8.85 months for the CD64 positive patients, while the median has not been reached in the CD64 negative patients. Multivariate analysis including CD64 expression and cytogenetic risk identified CD64 expression as an independent prognostic factor for survival and EFS, while cytogenetic-risk stratification became no longer a predictor.
Our data suggests that the expression of CD64 in pediatric AML is a significant independent poor prognostic factor in pediatric AML patients when treated with HSCT. Most of the CD64 positive patients die in their first year after HSCT and the management of these patients should be modified to address early death in this group of patients.
No relevant conflicts of interest to declare.
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