Acute myeloid leukemia with RAM immunophenotype: A report of three patients and comprehensive literature review.
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INTRODUCTION: The RAM immunophenotype (IP) in acute myeloid leukemia (AML) is defined by blasts with bright CD56 and weak-to-negative CD45, HLA-DR, and CD38 expression. A RAM IP predominantly presents in infants who have "standard-risk disease" under current criteria but, when treated accordingly, have devastatingly high rates of minimal residual disease and relapse with lower 3-year and overall survival rates. However, given the relative rarity of this phenotype, it is neither well-defined nor readily diagnosed. METHODS: We reviewed the electronic medical records of our institution from 1990 to 2024 for cases of AML expressing bright CD56 on flow cytometry and identified three cases with a RAM IP. Further, we performed a thorough literature search and reviewed impactful studies on pediatric AML and case/series reports of patients with a RAM IP, leading to the identification of 38 more cases. RESULTS: A total of 41 patients were collected. These patients were toddler age (1-3 years) with an equal sex distribution and clinically presented with low circulating blasts and cytopenias. Blasts were typically French-American-British M0 or M7. Immunophenotypically, CD33 and CD117 showed positivity in >90% of cases, with CD19, CD34, CD41, and CD42b, frequently positive. Half of the cases were positive for CD7 and CD61. T-cell/myeloid markers were rare, except for cytoplasmic CD3, seen in 1/3, apparently correlating with CBFAT2T3:GLIS1 fusions. Gains in chromosomes 21, 13, and 8 and CBFAT2T3::GLIS1 fusions were frequent. CONCLUSION: AML with a RAM IP has a poor prognosis. This study offers a detailed characterization of the clinicopathologic patterns associated with this rare entity, which may help formulate the most appropriate diagnostic approach.