Molecular Features of Three Children Diagnosed With Early T-Cell Precursor Acute Lymphoblastic Leukemia

Dear Editor, We describe the diagnostic characteristics of three pediatric patients with early T-cell precursor (ETP)-ALL. All three patients had hyperleukocytosis with a white blood cell (WBC) count of more than 100.0×10/L, showed immunophenotypic findings consistent with ETP-ALL, and were positive for FLT3 mutations. The clinical and laboratory findings, including immunophenotyping results (Fig. 1), T-cell receptor (TCR) rearrangements, Fms-related tyrosine kinase 3 (FLT3) mutations, and karyotype results, for the three patients are summarized in Table 1. The aim of this report is to provide information on ETP-ALL and reveal the immunophenotypic and molecular characteristics of ETP-ALL in pediatric patients. A 14-yr-old boy presented with dizziness, vomiting, and otalgia lasting for several weeks. Laboratory tests showed WBC count of 402.2×10/L, Hb of 8.4 g/dL, and platelet count of 78×10/L. A peripheral blood (PB) smear revealed a very high number of blasts (94% of nucleated elements). Bone marrow (BM) aspirates revealed 100% cellularity with 97% blasts. He received induction chemotherapy (vincristine, l-asparaginase, daunorubicin, dexamethasone, and intrathecal methotrexate) and achieved complete remission (CR). A 12-yr-old boy presented with left tibia pain for 14 days. Laboratory tests revealed WBC count of 130.1×10/L, Hb of 7.4 g/ dL, and platelet count of 33×10/L. A PB smear revealed that 75% of nucleated elements were leukemic blasts. BM aspirates revealed 100% cellularity with 99% blasts. After ALL induction chemotherapy, he achieved CR and received consolidation chemotherapy. A 12-yr-old boy presented with fever, cough, and petechiae of both tibiae for several weeks. Laboratory tests revealed WBC count of 169.5×10/L, Hb of 8.7 g/dL, and platelet count of 194×10/L. A PB smear revealed a markedly high number of blasts (89% of nucleated elements). He achieved CR after ALL induction chemotherapy. ETP-ALL is a T-ALL subtype with a very high risk of remission induction failure, relapse, and overall poor prognosis; it is characterized by a specific immunophenotype, i.e., CD1a(-), CD8(-), CD5 weak, with one or more stem cell or myeloid-associated markers [1, 2]. Our three patients showed very similar immunophenotypic patterns, with common expression of cCD3, T-cell markers (e.g., CD2 and CD7), and stem cell or myeloid/stem cell markers (e.g., CD34 and CD117) (Table 1). The myeloid marker CD13 was expressed in two patients and the myeloid/ monocytic marker CD64 was expressed in one patient. Although weak or negative CD5 was initially a part of the diagnostic criteria for ETP-ALL [1], the optimal aggregate of immunophenotypic markers for ETP leukemic cell identification is unknown. In a re-