Cytogenetic/molecular abnormalities associated with an unfavorable prognosis

AML with GATA2 or MECOM abnormalities (inv(3)(q21.3;q26.2)/t(3;3)(q21.3;q26.2) or t(3;21)(26.2;q22)). MECOM at chromosome 3q26 codes for two proteins, EVI1 and MDS1::EVI1, both of which are transcription regulators. The inv(3) and t(3;3) abnormalities lead to overexpression of EVI1 and to reduced expression of GATA2.[272,273] These abnormalities are associated with poor prognosis in adults with AML [209,274,275] but are rare in children (<1% of pediatric AML cases).[210,226,276]Abnormalities involving MECOM can also be detected in some AML cases with other 3q abnormalities (e.g., t(3;21)(26.2;q22)). The RUNX1::MECOM fusion is also associated with poor prognosis.[277,278]

AML with NPM1::MLF1 (t(3;5)(q25;q34)) gene fusions. This fusion results in a chimeric protein that includes virtually the entire MLF1 gene. This gene does not usually have a function in normal hematopoiesis, but in this context, it is hypothesized to result in ectopic expression of the protein. While incredibly rare in pediatrics (less than 0.5% of cases, most of which occur in adolescence),[279] it is generally associated with poor prognosis.[280]

AML with DEK::NUP214 (t(6;9)(p23;q34.1)) gene fusions. t(6;9) leads to the formation of a leukemia-associated fusion protein DEK::NUP214.[281,282] This subgroup of AML has been associated with a poor prognosis in adults with AML,[281,283,284] and occurs infrequently in children (less than 1% of AML cases). The median age of children with AML and DEK::NUP214 fusions is 10 to 11 years, and approximately 40% of pediatric patients have FLT3 ITD.[285,286]t(6;9) AML appears to be associated with a high risk of treatment failure in children, particularly for those not proceeding to allogeneic HSCT.[210,282,285,286]

AML with KAT6A::CREBBP (t(8;16)(p11.2;p13.3)) gene fusions (if 90 days or older at diagnosis). The t(8;16) translocation fuses the KAT6A gene on chromosome 8p11 to CREBBP on chromosome 16p13. It is associated with poor outcomes in adults, although its prognostic significance in pediatrics is less clear.[219,287] Although this translocation rarely occurs in children, in an iBFM AML study of 62 children, this translocation was associated with younger age at diagnosis (median, 1.2 years), FAB M4/M5 phenotype, erythrophagocytosis, leukemia cutis, and disseminated intravascular coagulation.[288] A substantial proportion of infants diagnosed with t(8;16) AML in the first month of life show spontaneous remission, although AML recurrence may occur months to years later.[288-291] These observations suggest that a watch-and-wait approach could be considered in cases of t(8;16) AML diagnosed in the neonatal period if close long-term monitoring can be ensured.[288] For older children, the prognosis is less favorable, and the typical recommendation is to proceed to HSCT once remission is achieved.

AML with FUS::ERG (t(16;21)(p11;q22)) gene fusions. In leukemias with t(16;21)(p11;q22), the FUS gene is joined with the ERG gene, producing a distinctive AML subtype with a gene expression profile that clusters separately from other cytogenetic subgroups.[292] This fusion is rare in pediatrics and represents 0.3% to 0.5% of pediatric AML cases. In a cohort of 31 patients with AML and FUS::ERG fusions, outcomes were poor, with a 4-year EFS rate of 7% and a cumulative incidence of relapse rate of 74%.[292]

AML with CBFA2T3::GLIS2 gene fusions. CBFA2T3::GLIS2 is a fusion resulting from a cryptic chromosome 16 inversion (inv(16)(p13.3;q24.3)).[293-297] It occurs commonly in non–Down syndrome AMKL, representing 16% to 27% of pediatric AMKL and presents at a median age of 1 year.[266,295,298-300] Leukemia cells with CBFA2T3::GLIS2 fusions have a distinctive immunophenotype (initially reported as the RAM phenotype),[301,302] with high CD56, dim or negative expression of CD45 and CD38, and a lack of HLA-DR expression. This fusion is a very high-risk lesion associated with poor clinical outcomes.[266,293,297-300]In a study of approximately 2,000 children with AML, the CBFA2T3::GLIS2 fusion was identified in 39 cases (1.9%), with a median age at presentation of 1.5 years. All cases observed in children were younger than 3 years.[303] Approximately one-half of cases had M7 megakaryoblastic morphology, and 29% of patients were Black or African American (exceeding the 12.8% frequency in patients lacking the fusion). Children with the fusion were found to be MRD positive after induction 1 in 80% of cases. In an analysis of outcomes from serial COG trials of 37 identified patients, OS at 5 years from study entry was 22.0% for patients with CBFA2T3::GLIS2 fusions versus 63.0% for fusion-negative patients (n = 1,724). Even worse outcomes were demonstrated when the subset of patients with CBFA2T3::GLIS2 AMKL were compared with patients with AMKL without the abnormality. Analysis from the COG AAML0531 and AAML1031 trials revealed OS rates of 43% (± 37%) and 10% (± 19%), respectively, among children with AMKL and this fusion.[300] As CBFA2T3::GLIS2 leukemias express high levels of cell surface FOLR1, a targetable surface antigen by immunotherapeutic approaches, the roles of such agents are planned for study in this high-risk population.[304,305]

AML with NUP98 gene fusions. NUP98 has been reported to form leukemogenic gene fusions with more than 20 different partners. A significant proportion of cases are associated with non–Down syndrome AMKL, although approximately 50% are seen outside of that morphologic subtype.[306,307] The two most common gene fusions in pediatric AML are NUP98::NSD1 and NUP98::KDM5A. In one report, the former fusion was observed in approximately 15% of cytogenetically normal pediatric AML cases, and the latter fusion was observed in approximately 10% of pediatric AMKL cases (see below).[266,295,300,308] AML cases with either NUP98 gene fusion show high expression of HOXA and HOXB genes, indicative of a stem cell phenotype.[282,295] Some of the less common fusions entail HOX genes.[307]The NUP98::NSD1 gene fusion, which is often cytogenetically cryptic, results from the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35).[282,308-310] This alteration occurs in approximately 4% to 7% of pediatric AML cases.[106,282,308,311,312] It is the most common NUP98 fusion seen. This disease phenotype is characterized by the following:A cytogenetically cryptic translocation, t(11;12)(p15;p13), results in the NUP98::KDM5A gene fusion.[314] Approximately 2% of all pediatric AML patients have NUP98::KDM5A fusions, and these cases tend to present at a young age (median age, 3 years).[315] Additional clinical characteristics are as follows:

AML with NUP98 gene fusions. NUP98 has been reported to form leukemogenic gene fusions with more than 20 different partners. A significant proportion of cases are associated with non–Down syndrome AMKL, although approximately 50% are seen outside of that morphologic subtype.[306,307] The two most common gene fusions in pediatric AML are NUP98::NSD1 and NUP98::KDM5A. In one report, the former fusion was observed in approximately 15% of cytogenetically normal pediatric AML cases, and the latter fusion was observed in approximately 10% of pediatric AMKL cases (see below).[266,295,300,308] AML cases with either NUP98 gene fusion show high expression of HOXA and HOXB genes, indicative of a stem cell phenotype.[282,295] Some of the less common fusions entail HOX genes.[307]The NUP98::NSD1 gene fusion, which is often cytogenetically cryptic, results from the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35).[282,308-310] This alteration occurs in approximately 4% to 7% of pediatric AML cases.[106,282,308,311,312] It is the most common NUP98 fusion seen. This disease phenotype is characterized by the following:A cytogenetically cryptic translocation, t(11;12)(p15;p13), results in the NUP98::KDM5A gene fusion.[314] Approximately 2% of all pediatric AML patients have NUP98::KDM5A fusions, and these cases tend to present at a young age (median age, 3 years).[315] Additional clinical characteristics are as follows:

The highest frequency of NUP98::NSD1 fusions in the pediatric population is observed in children aged 5 to 9 years (approximately 8%), with a lower frequency in younger children (approximately 2% in children younger than 2 years).

AML with NUP98 gene fusions. NUP98 has been reported to form leukemogenic gene fusions with more than 20 different partners. A significant proportion of cases are associated with non–Down syndrome AMKL, although approximately 50% are seen outside of that morphologic subtype.[306,307] The two most common gene fusions in pediatric AML are NUP98::NSD1 and NUP98::KDM5A. In one report, the former fusion was observed in approximately 15% of cytogenetically normal pediatric AML cases, and the latter fusion was observed in approximately 10% of pediatric AMKL cases (see below).[266,295,300,308] AML cases with either NUP98 gene fusion show high expression of HOXA and HOXB genes, indicative of a stem cell phenotype.[282,295] Some of the less common fusions entail HOX genes.[307]The NUP98::NSD1 gene fusion, which is often cytogenetically cryptic, results from the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35).[282,308-310] This alteration occurs in approximately 4% to 7% of pediatric AML cases.[106,282,308,311,312] It is the most common NUP98 fusion seen. This disease phenotype is characterized by the following:A cytogenetically cryptic translocation, t(11;12)(p15;p13), results in the NUP98::KDM5A gene fusion.[314] Approximately 2% of all pediatric AML patients have NUP98::KDM5A fusions, and these cases tend to present at a young age (median age, 3 years).[315] Additional clinical characteristics are as follows:

Patients with NUP98::NSD1 fusions present with a high white blood cell (WBC) count (median, 147 × 109/L in one study).[308,309] Most patients with AML and NUP98::NSD1 fusions do not show cytogenetic aberrations.[282,308] There is a slight male predominance for patients with this fusion (64.5% vs. 32.2%).[307]

AML with NUP98 gene fusions. NUP98 has been reported to form leukemogenic gene fusions with more than 20 different partners. A significant proportion of cases are associated with non–Down syndrome AMKL, although approximately 50% are seen outside of that morphologic subtype.[306,307] The two most common gene fusions in pediatric AML are NUP98::NSD1 and NUP98::KDM5A. In one report, the former fusion was observed in approximately 15% of cytogenetically normal pediatric AML cases, and the latter fusion was observed in approximately 10% of pediatric AMKL cases (see below).[266,295,300,308] AML cases with either NUP98 gene fusion show high expression of HOXA and HOXB genes, indicative of a stem cell phenotype.[282,295] Some of the less common fusions entail HOX genes.[307]The NUP98::NSD1 gene fusion, which is often cytogenetically cryptic, results from the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35).[282,308-310] This alteration occurs in approximately 4% to 7% of pediatric AML cases.[106,282,308,311,312] It is the most common NUP98 fusion seen. This disease phenotype is characterized by the following:A cytogenetically cryptic translocation, t(11;12)(p15;p13), results in the NUP98::KDM5A gene fusion.[314] Approximately 2% of all pediatric AML patients have NUP98::KDM5A fusions, and these cases tend to present at a young age (median age, 3 years).[315] Additional clinical characteristics are as follows:

A high percentage of patients with NUP98::NSD1 fusions (74%–90%) have co-occurring FLT3 ITD AML.[308,309,311]

AML with NUP98 gene fusions. NUP98 has been reported to form leukemogenic gene fusions with more than 20 different partners. A significant proportion of cases are associated with non–Down syndrome AMKL, although approximately 50% are seen outside of that morphologic subtype.[306,307] The two most common gene fusions in pediatric AML are NUP98::NSD1 and NUP98::KDM5A. In one report, the former fusion was observed in approximately 15% of cytogenetically normal pediatric AML cases, and the latter fusion was observed in approximately 10% of pediatric AMKL cases (see below).[266,295,300,308] AML cases with either NUP98 gene fusion show high expression of HOXA and HOXB genes, indicative of a stem cell phenotype.[282,295] Some of the less common fusions entail HOX genes.[307]The NUP98::NSD1 gene fusion, which is often cytogenetically cryptic, results from the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35).[282,308-310] This alteration occurs in approximately 4% to 7% of pediatric AML cases.[106,282,308,311,312] It is the most common NUP98 fusion seen. This disease phenotype is characterized by the following:A cytogenetically cryptic translocation, t(11;12)(p15;p13), results in the NUP98::KDM5A gene fusion.[314] Approximately 2% of all pediatric AML patients have NUP98::KDM5A fusions, and these cases tend to present at a young age (median age, 3 years).[315] Additional clinical characteristics are as follows:

In one of a series of COG studies, 108 children with NUP98::NSD1 fusions demonstrated lower rates of complete remission (CR) (38%, P < .001) and higher rates of MRD (73%, P < .001), compared with a cohort of patients without NUP98 fusions. Patients with NUP98::NSD1 fusions also had inferior EFS rates (17% vs. 47%; P < .001) and OS rates (36% vs. 64%; P < .001), compared with the reference cohort.[307] In another study that included children (n = 38) and adults (n = 7) with AML and NUP98::NSD1 fusions, presence of both NUP98::NSD1 fusions and FLT3 ITD independently predicted poor prognosis. Patients with both lesions had a low CR rate (approximately 30%) and a low 3-year EFS rate (approximately 15%).[309]

AML with NUP98 gene fusions. NUP98 has been reported to form leukemogenic gene fusions with more than 20 different partners. A significant proportion of cases are associated with non–Down syndrome AMKL, although approximately 50% are seen outside of that morphologic subtype.[306,307] The two most common gene fusions in pediatric AML are NUP98::NSD1 and NUP98::KDM5A. In one report, the former fusion was observed in approximately 15% of cytogenetically normal pediatric AML cases, and the latter fusion was observed in approximately 10% of pediatric AMKL cases (see below).[266,295,300,308] AML cases with either NUP98 gene fusion show high expression of HOXA and HOXB genes, indicative of a stem cell phenotype.[282,295] Some of the less common fusions entail HOX genes.[307]The NUP98::NSD1 gene fusion, which is often cytogenetically cryptic, results from the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35).[282,308-310] This alteration occurs in approximately 4% to 7% of pediatric AML cases.[106,282,308,311,312] It is the most common NUP98 fusion seen. This disease phenotype is characterized by the following:A cytogenetically cryptic translocation, t(11;12)(p15;p13), results in the NUP98::KDM5A gene fusion.[314] Approximately 2% of all pediatric AML patients have NUP98::KDM5A fusions, and these cases tend to present at a young age (median age, 3 years).[315] Additional clinical characteristics are as follows:

In a study of children with refractory AML, NUP98 was overrepresented compared with a cohort who did achieve remission (21% [6 of 28 patients] vs. <4%).[313]

AML with NUP98 gene fusions. NUP98 has been reported to form leukemogenic gene fusions with more than 20 different partners. A significant proportion of cases are associated with non–Down syndrome AMKL, although approximately 50% are seen outside of that morphologic subtype.[306,307] The two most common gene fusions in pediatric AML are NUP98::NSD1 and NUP98::KDM5A. In one report, the former fusion was observed in approximately 15% of cytogenetically normal pediatric AML cases, and the latter fusion was observed in approximately 10% of pediatric AMKL cases (see below).[266,295,300,308] AML cases with either NUP98 gene fusion show high expression of HOXA and HOXB genes, indicative of a stem cell phenotype.[282,295] Some of the less common fusions entail HOX genes.[307]The NUP98::NSD1 gene fusion, which is often cytogenetically cryptic, results from the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35).[282,308-310] This alteration occurs in approximately 4% to 7% of pediatric AML cases.[106,282,308,311,312] It is the most common NUP98 fusion seen. This disease phenotype is characterized by the following:A cytogenetically cryptic translocation, t(11;12)(p15;p13), results in the NUP98::KDM5A gene fusion.[314] Approximately 2% of all pediatric AML patients have NUP98::KDM5A fusions, and these cases tend to present at a young age (median age, 3 years).[315] Additional clinical characteristics are as follows:

Cases with NUP98::KDM5A fusions tend to be AMKL (34%), followed by FAB M5 (21%), and FAB M6 (17%) histologies.[315] NUP98::KDM5A fusions are observed in approximately 10% of pediatric AMKL cases,[266,298] and patients with this fusion tend to present with lower WBC counts than patients with NUP98::NSD1 fusions.

AML with NUP98 gene fusions. NUP98 has been reported to form leukemogenic gene fusions with more than 20 different partners. A significant proportion of cases are associated with non–Down syndrome AMKL, although approximately 50% are seen outside of that morphologic subtype.[306,307] The two most common gene fusions in pediatric AML are NUP98::NSD1 and NUP98::KDM5A. In one report, the former fusion was observed in approximately 15% of cytogenetically normal pediatric AML cases, and the latter fusion was observed in approximately 10% of pediatric AMKL cases (see below).[266,295,300,308] AML cases with either NUP98 gene fusion show high expression of HOXA and HOXB genes, indicative of a stem cell phenotype.[282,295] Some of the less common fusions entail HOX genes.[307]The NUP98::NSD1 gene fusion, which is often cytogenetically cryptic, results from the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35).[282,308-310] This alteration occurs in approximately 4% to 7% of pediatric AML cases.[106,282,308,311,312] It is the most common NUP98 fusion seen. This disease phenotype is characterized by the following:A cytogenetically cryptic translocation, t(11;12)(p15;p13), results in the NUP98::KDM5A gene fusion.[314] Approximately 2% of all pediatric AML patients have NUP98::KDM5A fusions, and these cases tend to present at a young age (median age, 3 years).[315] Additional clinical characteristics are as follows:

Other genetic aberrations associated with pediatric AML, including FLT3 variants, are uncommon in patients with NUP98::KDM5A fusions.[315]

AML with NUP98 gene fusions. NUP98 has been reported to form leukemogenic gene fusions with more than 20 different partners. A significant proportion of cases are associated with non–Down syndrome AMKL, although approximately 50% are seen outside of that morphologic subtype.[306,307] The two most common gene fusions in pediatric AML are NUP98::NSD1 and NUP98::KDM5A. In one report, the former fusion was observed in approximately 15% of cytogenetically normal pediatric AML cases, and the latter fusion was observed in approximately 10% of pediatric AMKL cases (see below).[266,295,300,308] AML cases with either NUP98 gene fusion show high expression of HOXA and HOXB genes, indicative of a stem cell phenotype.[282,295] Some of the less common fusions entail HOX genes.[307]The NUP98::NSD1 gene fusion, which is often cytogenetically cryptic, results from the fusion of NUP98 (chromosome 11p15) with NSD1 (chromosome 5q35).[282,308-310] This alteration occurs in approximately 4% to 7% of pediatric AML cases.[106,282,308,311,312] It is the most common NUP98 fusion seen. This disease phenotype is characterized by the following:A cytogenetically cryptic translocation, t(11;12)(p15;p13), results in the NUP98::KDM5A gene fusion.[314] Approximately 2% of all pediatric AML patients have NUP98::KDM5A fusions, and these cases tend to present at a young age (median age, 3 years).[315] Additional clinical characteristics are as follows:

Prognosis for children with NUP98::KDM5A fusions is inferior to that of other children with AML (5-year EFS rate, 29.6% ± 14.6%; OS rate, 34.1% ± 16.1%) in one series.[315] Another study that included 32 patients with NUP98::KDM5A fusions demonstrated similar CR rates to the reference population but inferior OS (30%, P < .001) and EFS rates (25%; P = .01).[307]

AML with 12p13.2 rearrangements (ETV6 and any partner gene). The ETS family of genes encode transcription factors responsible for cellular growth and development. The ETV6 gene encodes a transcription factor that serves as a tumor suppressor gene and is the most frequent ETS family rearranged partner in pediatric AML. The cryptic translocation t(7;12)(q36;p13) encodes ETV6::MNX1, the most frequent ETV6-rearranged fusion partner, which occurs in approximately 1% of pediatric AML cases (enriched in infants). It is associated with poor clinical outcomes.[316] It is also strongly associated with trisomy 19.[316] The transcription may be cryptic by conventional karyotyping and, in some cases, may be confirmed only by fluorescence in situ hybridization (FISH).[317,318] This alteration occurs virtually exclusively in children younger than 2 years, with a median age of diagnosis of 6 months.[316] It appears to be associated with a high risk of treatment failure.[210,211,249,317,319,320] A literature review of 17 cases showed a 3-year EFS rate of 24% and OS rate of 42%.[219,316,321]

AML with 12p deletion to include 12p13.2 (loss of ETV6). ETV6 deletions are exceedingly rare in pediatric AML. In one pediatric series, 4 of 259 patients (1.5%) had an ETV6 deletion.[321,322] This abnormality is enriched in adult patients with chromosome 7 abnormalities and in patients with TP53 variants.[323] However, in a second pediatric series, there was a reported correlation with CBF AML.[322] According to this latter series, relapse risk rates for patients with and without deletions in ETV6 were 63% and 45%, respectively (P = .3), with corresponding disease-free survival (DFS) rates of 32% and 53%, respectively (P = .2). However, there was a high prevalence of CBF AML in patients with ETV6 deletions. In the context of CBF AML, the deletion was associated with adverse outcomes. Patients with CBF AML, with and without ETV6 deletions, had EFS rates of 0% and 63%, respectively (P = .002). Of the patients with CBF AML who achieved an initial CR, those with an ETV6 deletion had a risk of relapse rate of 88%, compared with 38% for those without the deletion (P = .08). The corresponding DFS rates were 0% for patients with an ETV6 deletion, compared with 61% for those without the deletion (P = .009).[322]

Chromosome 5 and 7 abnormalities. Chromosomal abnormalities associated with poor prognosis in adults with AML include those involving chromosome 5 (del(5q)) and chromosome 7 (monosomy 7).[209,274,324] These cytogenetic subgroups represent approximately 2% and 4% of pediatric AML cases, respectively, and are also associated with poor prognosis in children.[210,274,324-327] Chromosome 5 and 7 abnormalities appear to lack prognostic significance in AML patients with Down syndrome who are aged 4 years and younger.[328]Increasing data show that the presence of monosomy 7 is associated with a higher risk of a patient having germline GATA2, SAMD9 or SAMD9L pathogenic variants. Cases associated with an underlying RUNX1-altered familial platelet disorder, telomere biology disorder, and germline ERCC6L2 pathogenic variants have also been reported.[329] Germline testing should be considered when monosomy 7 disease is identified.In the past, patients with del(7q) were also considered to be at high risk of treatment failure, and data from adults with AML support a poor prognosis for both del(7q) and monosomy 7.[212] However, outcome for children with del(7q), but not monosomy 7, appears comparable to that of other children with AML.[211,326] The presence of del(7q) does not abrogate the prognostic significance of favorable cytogenetic characteristics (e.g., inv(16) and t(8;21)).[209,326]

AML with 10p12.3 rearrangements (MLLT10::any partner gene). MLLT10 frequently forms fusions with partners other than KMT2A, and these fusions are also associated with a poor prognosis. A retrospective review of 2,226 children enrolled in serial COG trials identified 23 children with non-KMT2A::MLLT10 fusions. Nearly one-half of patients (13 of 23) had MLLT10::PICALM fusions, and the EFS rate of this heterogenous group was 12.7%.[330] Another study focused on the prognostic impact of the MLLT10::PICALM fusion, which results in aberrant hematopoiesis and loss of chromatin-mediated gene regulation. Within this specific subset, the 20 pediatric patients with MLLT10::PICALM fusions had a poor prognosis. The 5-year EFS rate was 22%, and the OS rate was 26%.[331]

FLT3 variants. Presence of a FLT3 ITD variant appears to be associated with poor prognosis in adults with AML,[332] particularly when both alleles are altered or there is a high ratio of the variant allele to the normal allele.[333] FLT3 ITD variants also convey a poor prognosis in children with AML.[217,250,334-336] The frequency of FLT3 ITD variants in children is lower than that observed in adults, especially for children younger than 10 years, for whom 5% to 10% of cases have the variant (compared with approximately 30% in adults).[335,336] The prevalence of FLT3 ITD is increased in certain genomic subtypes of pediatric AML, including cases with the NUP98::NSD1 gene fusion, 80% to 90% of which have a co-occurring FLT3 ITD.[308,309]The prognostic significance of FLT3 ITD is modified by the presence of other recurring genomic alterations.[308,309] For patients who have FLT3 ITD, the presence of either WT1 variants or NUP98::NSD1 fusions is associated with poorer outcomes (EFS rates below 25%) than for patients who have FLT3 ITD without these alterations.[219] Conversely, a co-occurring cryptic DEK::NUP214 fusion may be more favorable, particularly with the addition of a FLT3 inhibitor to standard front-line chemotherapy. When FLT3 ITD is accompanied by NPM1 variants, the outcome is relatively favorable and is similar to that of pediatric AML cases without FLT3 ITD.[219] The latter subset is the one scenario in which the presence of the FLT3 ITD variant does not necessarily upstage a patient to high risk, based on the favorable outcomes seen with the co-occurring variants.[219]Activating single nucleotide variants of FLT3 have also been identified in both adults and children with AML, although the clinical significance of these variants is not clearly defined. Some of these single nucleotide variants appear to be specific to pediatric patients.[219]

RAM phenotype. The RAM phenotype is characterized by high-intensity CD56 expression, dim-to-negative expression of CD45 and CD38, and a lack of HLA-DR expression. These patients tend to be younger, with a median age of 1.6 years in the initially reported series. This phenotype is enriched in patients with non-Down syndrome–related AMKL.[337] Clinically, patients with the RAM phenotype have inferior outcomes. In the initial series, patients in the RAM cohort had a 3-year EFS rate of 16%, compared with 51% for patients in the non-RAM cohort (P < .001). Patients in the RAM cohort also had inferior survival compared with patients with high CD56 expression, who lacked other phenotypic features of the RAM phenotype. OS was also inferior compared with the patients without the RAM phenotype (26% vs. 69%, P = .001). In a subanalysis, the OS of the patients in the RAM cohort was also markedly worse than patients in the CD56-positive (non-RAM) cohort (26% vs. 66%, P < .001) and the CD56-negative cohort (26% vs. 70%, P < .001).[337] Many, but not all, patients with a RAM phenotype have evidence of a CBFA2T3::GLIS2 fusion that, in itself, confers very high-risk disease. In a published series, approximately 60% of patients with the RAM phenotype at diagnosis were subsequently found to have this cryptic fusion that also confers higher-risk disease.[337]