einstein (São Paulo). 08/Mar/2016;14(2):288-9.

Immunophenotypic evolution of blast populations in pediatric acute myeloid leukemia

DOI: 10.1590/S1679-45082016AI3516

Acute myeloid leukemia (AML) results from accumulation of abnormal blasts in the bone marrow, interfering with hematopoiesis.⁽⁾ Multiparametric flow cytometry is an important and well-known tool for AML diagnosis and for monitoring of minimal residual disease.⁽⁾ However, this technique is still poorly explored to elucidate clonal evolution of the leukemia. We present laboratory observations of a pediatric AML case whose multiparametric flow cytometry data provided evidences of clonal history of leukemia from the diagnosis through relapses episodes.

A 7-year-old patient, diagnosed as AML with maturation, with complex karyotype, wild type FLT3, negative for 11q23, inv(16), t(9;22), and for t(8;21). Flow cytometry analysis showed two distinct subpopulations of CD34(+) blasts in the bone marrow, with 72.5% of blasts expressing CD34/CD33/CD117/CD11b/CD56, and 16.1% expressing the same markers with additional CD7. After treatment, minimal residual disease was monitored until the achievement of immunophenotypic remission. Six months after starting therapy, the patient relapsed with 75.1% of blasts in the bone marrow, divided into three separate subpopulations: 42% expressing CD34/CD117/CD11b/CD56/CD7 (this population persisted from the diagnosis), 22.5% expressing high levels of the B-cell marker CD19, and a third one expressing lower levels of CD19 (10.5% of the cells). Unlike the diagnosis profile, all clones were CD7(+) ( to ). The treatment reduced the leukemia burden to 0.04% and unrelated-donor bone marrow transplantation (matched unrelated donor) was performed. Three months after bone marrow transplantation, the patient relapsed with 62.9% of blasts in the bone marrow, in which all expressed CD19 but represented in two distinct immunophenotypic populations: CD34/CD33/CD117/CD11b/CD19/CD56/CD7 (40%) and another lacking CD56 and CD7 (22.9%) (). After additional chemotherapy, the patient had persistent disease. In the last evaluation we found 39.7% of blasts in the bone marrow expressing CD7/CD56/CD19 and cytoplasmic CD3. A small fraction (5%) of these cells presented lower levels of CD19, suggestive of a distinct subpopulation (). Interestingly, both populations lacked myeloperoxidase expression, although have maintained the other original myeloid markers (CD33/CD117/CD11b). Monitoring the immunophenotype of the blasts during the progression of the AML allowed us to assume the clone history of the disease, which revealed the complexity of this case (). Under chemotherapy, we observed the complete disappearance of some blast populations, whereas others persisted and originated new subpopulations in the following relapse.

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