Acute Myeloid Leukemia (AML) with t(6;9)(p23;q34) Defines a Very Poor Risk Leukemia Subgroup with Distinguishing Clinicopathological Features: A United States (US) Cytogenetics Intergroup Study of 62 AML and MDS Cases.
Authors: Slovak Marilyn L. , Bloomfield Clara D. , Gundacker Holly , Dewald Gordon , Appelbaum Frederick R. , Larson Richard A. , Tallman Martin S. , Willman Cheryl , Ravindranath Yaddanapudi , Alonzo Todd A. , Carroll Andrew , Hirsch Betsy , Raimondi Susana , Heerema Nyla A. 
Published: April 2020

Abstract
The t(6;9)(p23;q34) translocation, which results in the formation of a chimeric fusion gene DEK/CAN on the der(6) chromosome, is a rare recurring cytogenetic aberration reported in patients (pts) with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Because the abnormality is an infrequent finding in AML with most reports describing 2 to 8 cases, the US Intergroup Cytogenetics Consortium investigated the frequency and clinical, pathologic and cytogenetic characteristics of t(6;9) leukemia among pts registered to 19 different treatment protocols. Among 6567 pts with evaluable karyotypes, 62 (0.9%) had t(6;9): 30 on pediatric trials (mean 12 yrs; 15/15 male/female) and 32 on adult trials (mean 38 yrs; 21/11 male/female), compared to the mean age of 8 yrs for pts on pediatric AML/MDS trials and 54 yrs for pts on adult AML/MDS trials. Three cases (5%) showed a complex (3- or 4-way) variant translocation and only 7 (11%) of the 62 pts showed secondary aberrations: 3 (10%) of 30 pediatric cases and 4 (13%) of 32 of the adult cases. The majority of t(6;9) cases were classified as FAB-M2 (34%), M4 (31%) or M1 (19%). Although the immunophenotyping (N=7) and morphology data (N=17) were limited, increased basophilia and Auer rods were observed and the blasts showed CD13, CD15, and CD33 expression, in agreement with a previously reported preliminary study (Am J Clin Pathol107:430–437,1997). Four pts (1 pediatric and 3 adults) had MDS. Among the remaining 58 pts, 25 (78%) adults had previously untreated AML (16 de novo, 2 secondary, and 7 unknown secondary/de novo status) while all 29 pediatric AML patients had de novo AML. For the 54 patients with previously untreated AML, complete remission rates were slightly higher, but not statistically significantly (p=.20) in children (69%), when compared to adults (52%). Disease-free survival (DFS) (combined median 8.8 mo, 95% CI, 5.1–13.7) and overall survival (OS) (combined median 11.9 mo, 95% CI, 10.0–14.3) were poor regardless of age, a finding in distinct contrast to the t(8:21) favorable risk group also commonly observed in M2/M4 AML. Kaplan-Meier estimates of 3-yr survival were 25% for pediatric cases and 9% for adults. Analysis of stem cell transplantation (SCT) was inconclusive due to the small number of transplanted patients (N=15), but suggested that allogeneic SCT might be associated with better OS than no SCT (hazard ratio [HR] 0.39 after SCT, 95% CI 0.14 – 1.11), while autologous SCT might not (HR 1.49, 95% CI 0.57–3.85). Based on this study of t(6;9), largest to date and previously published data, AML with t(6;9) leukemia is a distinct AML subgroup with distinguishing clinicopathological features including poor outcome in relatively young patients, not explained by other known poor prognostic factors that warrants novel therapeutic strategies. Similar to other recurring cytogenetic abnormality subtypes of de novo acute myeloid leukemia of the WHO classification, t(6;9) may warrant a specific leukemia disease subtype.