Medicosnext
Dr. Prahar Dahal is a clinically oriented Consultant Pathologist with advanced fellowship training in cancer cytogenetics holding an MD in Pathology and a Master’s degree in Healthcare Management. He has expertise in solid tumor FISH, FISH for leukemia and multiple myeloma, cancer karyotyping and
molecular genetics tests related to leukemia and solid tumor. He can integrate high quality diagnostic
cytogenetics with effective laboratory and healthcare operations management. His work emphasizes
accurate reporting, robust quality assurance systems, multidisciplinary collaboration, and evidence-
based oncologic patient care.
The TakeAway Message
When a child fights leukemia, the true battleground is hidden deep within their genetic code,
distinct from the battles fought by adults. Pediatric Acute Myeloid Leukemia is a rare blood
cancer that affects children differently than older patients, boasting much higher recovery rates
with nearly 90% of children achieving remission. In the past, doctors diagnosed this disease
primarily by counting the number of immature cells, known as blasts, under a microscope.
However, the World Health Organization has revolutionized this approach. Today, the diagnosis
is no longer a numbers game only; it is based on identifying specific cytogenetic or molecular
genetics abnormality too. This means a child can be diagnosed and treated earlier based on a
single genetic clue, even if their blast count does not meet the old threshold in most of the cases.
Understanding these genetic blueprints is the key to saving lives without causing unnecessary harm.
Because children are not simply miniature adults, the “risk scorecards” used for older patients do not
apply to them. Instead, doctors classify children into standard, intermediate, or high risk groups based
on their specific chromosomal makeup. Some genetic changes, such as those found in “Core Binding
Factor” leukemia, signal a high chance of cure with standard treatment. Others, like most cases of
KMT2A gene rearrangement or a complex karyotype, serve as red flags that the cancer is aggressive and may require a bone marrow transplant. By decoding these genetic patterns, doctors can tailor
treatments precisely—giving intense therapy only to those who truly need it while sparing others from
harsh side effects.
Pediatric acute myeloid leukemia (pAML) is a rare but clinically significant malignancy, with an incidence of approximately seven cases per million children under the age of fifteen and a median age at diagnosis of six years. Infant AML has recently been redefined to include all children under two years of age because of shared biological and clinical characteristics. Compared with adults, children with AML have substantially better outcomes, with complete remission rates approaching 90%. These favorable outcomes are largely attributed to differences in disease biology and cytogenetic profiles.
The World Health Organization (WHO) 5th edition classification of AML emphasizes genetic abnormalities over morphology. The traditional category of AML not otherwise specified (NOS) has been eliminated, and AML is now categorized primarily by defining genetic abnormalities, differentiation, and other emerging genetic alterations. Importantly, the historical requirement of at least 20% blasts for AML diagnosis has been removed for most AML types with defining genetic abnormalities, except for AML with BCR::ABL1 fusion and AML with CEBPA mutation, which still require the blast threshold.
Risk stratification is a cornerstone of pAML management. Its goals are to tailor treatment intensity, minimize toxicity, and identify targetable lesions for precision therapy. Adult risk classification systems, such as the European LeukemiaNet (ELN), cannot be directly applied to children because cytogenetic and molecular risk associations differ significantly by age. In pediatric AML, three prognostic categories are generally recognized: favorable, intermediate, and adverse. Favorable risk is associated with a five-year survival exceeding 70% in children, intermediate risk with survival between 50% and 70%, and adverse risk with survival below 50%.
KMT2A rearrangements pediatric AML represent a large and heterogeneous subgroup. Outcomes of KMT2A rearranged pediatric AML vary significantly depending on the fusion partner, French–American–British (FAB) subtype, and the presence of additional cytogenetic abnormalities. Poor prognostic groups include 9p22/KMT2A::MLLT3, 19p13.3/KMT2A::MLLT1, 10p12/KMT2A::MLLT10, 10p11.2/KMT2A::ABl1, 4q21/KMT2A::AFF1, 6q27/KMT2A::AFDN. Children with 9p22/KMT2A::MLLT3rearrangements and FAB-M5 morphology have superior event-free survival (EFS) and overall survival (OS), whereas the presence of trisomy 6 is associated with inferior outcomes. Other KMT2A-rearranged subgroups, such as KMT2A::SEPT6 and KMT2A::EPS15, are associated with relatively favorable prognosis.
Acute promyelocytic leukemia (APML) with PML::RARA fusion is a distinct entity with excellent outcomes when treated with all-trans retinoic acid (ATRA) and chemotherapy. However, studies have shown that the presence of more than two additional chromosomal abnormalities increases the risk of relapse, underscoring the importance of comprehensive cytogenetic evaluation even in favorable subtypes.
Core binding factor (CBF) AML is the most common favorable-risk subgroup in children and includes AML with RUNX1::RUNX1T1 and CBFB::MYH11 fusions. These leukemias typically occur in children aged eight to nine years and are rare in infants. Although overall survival exceeds 80%, relapse rates remain around 30%, highlighting the need for vigilant monitoring and potential therapy optimization.
Several rare but clinically important cytogenetic abnormalities are associated with poor prognosis in pAML. These include AML with MECOM rearrangements, DEK::NUP214 fusion, and NUP98 rearrangements such as NUP98::KDM5A and ETV6::MNX1. These entities often present in younger children, are associated with aggressive disease biology, and frequently require intensified therapy or hematopoietic stem cell transplantation.
Acute megakaryoblastic leukemia (AMKL) in non-Down syndrome children is another high-risk subgroup. It commonly affects infants, shows a female predominance, and is frequently associated with additional chromosomal abnormalities such as hyperdiploidy and trisomy 21. The inv(16)(p13.3q24.3)/CBFA2T3-GLIS2 fusion is particularly associated with poor outcomes, with overall survival rates as low as 15–30%.
Unbalanced chromosomal abnormalities also have significant prognostic implications. Monosomy 7 and deletion 7q are among the most studied abnormalities. Monosomy 7 is associated with poor prognosis, with five-year overall survival around 35%, whereas del(7q) carries an intermediate risk. Monosomy 5 and deletion 5q are rare in children but are strongly associated with complex karyotypes, rapid disease progression, and very poor outcomes.
Hyperdiploidy in childhood AML is relatively uncommon and often associated with younger age and AML-M7 subtype. Most hyperdiploid cases have modal chromosome numbers between 50 and 52. Overall survival is similar to that of non-hyperdiploid AML, although specific chromosomal gains influence prognosis: trisomy 8 is associated with favorable outcomes, whereas trisomy 21 confers inferior survival.
Complex karyotypes, defined as three or more unrelated chromosomal abnormalities, have a markedly adverse prognostic impact in adults but appear less uniformly adverse in children. Studies suggest that the prognostic significance of karyotype complexity in pAML is influenced by the specific pattern of abnormalities rather than complexity alone. In contrast, monosomal karyotypes, characterized by multiple autosomal monosomies or a monosomy with additional structural abnormalities, are consistently associated with very poor outcomes in children, particularly when accompanied by hypodiploidy.
Large international studies have demonstrated that specific cytogenetic abnormalities at diagnosis also predict outcomes after hematopoietic stem cell transplantation in poor-risk pAML. Children with certain high-risk cytogenetic features have lower relapse rates and improved leukemia-free survival following transplant, emphasizing the role of cytogenetics in transplant decision-making.
In conclusion, cytogenetic analysis is indispensable in pediatric AML for accurate diagnosis, classification, prognostic stratification, and treatment planning. Pediatric AML is biologically distinct from adult AML, with a higher frequency of balanced chromosomal rearrangements and generally more favorable outcomes. Continued refinement of cytogenetic and molecular risk stratification will further improve personalized therapy and long-term survival for children with AML.
