Acute myeloid leukemia with RAM immunophenotype: A new underdiagnosed entity

Area of Science:

• Hematology
• Pediatric Oncology
• Immunophenotyping

Background:

• Acute myeloid leukemia (AML) with RAM immunophenotype is a distinct subtype characterized by strong CD56 expression and poor response to chemotherapy.
• This aggressive leukemia subtype presents diagnostic challenges due to its unique morphological and immunophenotypic properties.

Purpose of the Study:

• To analyze the clinical, morphological, immunophenotypic, cytogenetic, and molecular profiles of pediatric AML cases with RAM immunophenotype.
• To identify diagnostic challenges and prognostic factors associated with this AML subtype.

Main Methods:

• Retrospective analysis of seven newly diagnosed pediatric AML cases (age <18 years) with RAM immunophenotype from January 2019 to December 2021.
• Comprehensive evaluation including morphology, cytochemistry, immunophenotyping (flow cytometry), cytogenetics, and molecular studies.
• Clinical follow-up of patients' disease and treatment status.

Main Results:

• Seven cases (2.3%) of pediatric AML with RAM immunophenotype were identified, with ages ranging from 9 months to 5 years.
• Two cases were initially misdiagnosed as granulocytic sarcoma due to strong CD56 positivity and lack of leukocyte common antigen.
• Flow cytometry revealed characteristic findings including low side scatter, dim/negative CD45 and CD38, and bright CD56; weak CD13 expression was noted.
• Six out of seven patients (85.7%) succumbed to the disease within 3-343 days.

Conclusions:

• AML with RAM immunophenotype is a distinct pediatric AML subtype with a poor prognosis and potential diagnostic challenges, especially when presenting as a soft tissue mass.
• Comprehensive immunophenotypic evaluation is crucial for accurate diagnosis of myeloid sarcoma with RAM immunophenotype.
• Weak CD13 expression is identified as an additional diagnostic finding for this AML subtype.