Acute Promyelocytic Leukemia With a Subgroup Exhibiting Basophilic Differentiation

A 66‐year‐old man presented with dizziness and fatigue. Peripheral blood counts revealed a white blood cell count of 2.38 × 10⁹/L, hemoglobin of 97 g/L, and a platelet count of 128 × 10⁹/L. Peripheral blood smear showed 6% abnormal promyelocytes. Bone marrow aspirate demonstrated 55% abnormal promyelocytes and 7% basophils (Figure 1A,B). Flow cytometric analysis of the bone marrow identified an abnormal early myeloid population comprising 24.75% of nucleated cells, with the following immunophenotype: CD45dim, CD34⁻, HLA‐DR⁻, CD117⁺, CD33⁺⁺, CD13⁺, CD19⁻, CD11b⁻, CD10⁻, CD38⁻, CD15⁻, CD16⁻, CD14⁻, CD7⁻, CD36⁻, CD56⁻, CD64dim, CD4⁻, cyCD79a⁻, cyCD3⁻, and cyMPO⁺. A distinct basophil population accounting for 20.50% of cells was also detected, exhibiting the phenotype: CD45⁺, CD34⁻, HLA‐DR⁻, CD117dim, CD203c⁺, CD11b⁺, CD9⁺, CD33⁺⁺, CD13⁺, CD10⁺, and CD2dim (Figure 1C). Karyotypic analysis revealed 46,XY,?t(15;17)(q24;q21), and molecular studies confirmed the presence of the PML::RARA fusion gene. A diagnosis of acute promyelocytic leukemia (APL) was established. The patient was treated with all‐trans retinoic acid (ATRA) in combination with arsenic trioxide, with hydroxyurea administered to control the white blood cell count during induction. Bone marrow evaluation at 1 month confirmed remission.

FIGURE 1.

Cytomorphologic and flow cytometric findings. (A, B) Bone marrow smear revealed 55% abnormal promyelocytes and 7% basophils (Wright‐Giemsa stain, ×100 objective). Myeloperoxidase staining was strongly positive in both cell populations. Basophilic granules were visible within a subset of the promyelocytes. Panel (B) showing from left to right: A typical promyelocyte, a promyelocyte with basophilic granules, and a basophil. (C) Flow cytometric analysis identified a basophil population.

Basophilic differentiation is common in AML with t(6;9)(p22.3;q34.1)/DEK::NUP214, but rarely reported in other AML subtypes, such as those with myelodysplasia‐related cytogenetic abnormalities [1]. APL with basophilic differentiation is seldom reported [2]. Matarraz et al. studied 109 newly diagnosed and untreated APL patients and found that cases with CD203c expression (levels of positivity on leukemic cells ranging from 0.6% to 45%) accounted for 30%, but only two patients had expression rates exceeding 20%. In our case, the expression rate was 20.5% [3]. In this case, morphologic assessment showed a low percentage of typical mature basophils, while a proportion of leukemic promyelocytes contained basophilic granules. Flow cytometry revealed a prominent population of cells exhibiting a basophil immunophenotype, which also expressed CD117, suggesting an early stage of basophilic differentiation. These findings indicate that the flow‐cytometrically defined basophil population likely corresponds to the morphologically identified granulated APL cells.

Funding

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.