Acute myelogenous leukemia switch lineage upon relapse to acute lymphoblastic leukemia: a case report

Abstract

Acute leukemia, the most common form of cancer in children, accounts for approximately 30% of all childhood malignancies, with acute lymphoblastic leukemia being five times more frequent than acute myeloid leukemia. Lineage switch is the term that has been used to describe the phenomenon of acute leukemias that meet the standard French-American-British system criteria for a particular lineage (either lymphoid or myeloid) upon initial diagnosis, but meet the criteria for the opposite lineage at relapse. Many reports have documented conversions of acute lymphoblastic leukemia to acute myeloid leukemia. Here, we report the case of a 4-year-old child with acute myeloid leukemia, which upon relapse switched to acute lymphoblastic leukemia. The morphologic, phenotypic, and molecular features suggest the origin of a new leukemic clone.

Figure 1

Bone marrow aspiration at AML diagnosis. Blast cells were large in size and had a low nucleus:cytoplasm ratio, monocytoid aspect, and blue-gray cytoplasm. Wright stain, 1000×.

Figure 2

Flow cytometry AML at diagnosis. Immunophenotyping of leukemic cells by flow cytometric analyses revealed myeloid blasts negative for CD10 and CD19 (A) but positive for CD13 (B) and CD14 (C).

Figure 3

Bone marrow aspiration at relapse. Blasts were smaller, with a predominance of small cells, scanty cytoplasm, moderate cytoplasmic basophilia, and variable cytoplasmic vacuolation. Wright stain, 1000×.

Figure 4

Flow cytometry at relapse. Flow cytometric analyses of leukemic cells at relapse. Blast cells were identified as lymphoblasts because the immunophenotype was positive for CD10 and CD19 (A) but negative for CD13 and CD14 (B, C).

Figure 5

PAX5 expression in bone marrow from pro-B ALL at AML remission. Immunohistochemistry for PAX5 was performed on a marrow biopsy. The frequency of PAX5 cells was 15% (A, B). PAX5 expression by lymph node germinal center cells is shown for control (C, D).