Acute Myeloid Leukemia With t(8;21)/RUNX1-RUNX1T1 demonstrate a High Number Of Secondary Genetic Lesions: Frequency and Impact On Clinical Outcome

Translocation t(8;21) with the resulting RUNX1-RUNX1T1 rearrangement is one of the most common chromosomal abnormalities in acute myeloid leukemia (AML). Although it is generally associated with a favourable prognosis, many additional genetic lesions may impact on outcome.

To assess the frequency and clinical impact of additional mutations and chromosomal aberrations in AML with t(8;21)/RUNX1-RUNX1T1.

We analyzed 139 patients (pts) who were referred to our laboratory for diagnosis of AML between 2005 and 2012 (65 females, 74 males; median age 53.3 years, range 18.6 - 83.8 years). All pts were proven to have t(8;21)/RUNX1-RUNX1T1 by a combination of chromosome banding analysis, fluorescence in situ hybridisation and RT-PCR. Analysis of mutations in ASXL1, FLT3-TKD, KIT (D816, exon8-11), NPM1, IDH1 and IDH2, KRAS, NRAS, CBL, and JAK2 as well as of MLL-PTD and FLT3-ITD was performed in all pts.

107/139 pts were classified according to FAB criteria (77.0%). 34/107 had AML M1 (31.8%) and 73/107 AML M2 (68.2%). 117/139 had de novo AML (84.2%), 22/139 had therapy-related AML (t-AML) (15.8%). 69/139 (49.6%) pts had at least one molecular alteration in addition to RUNX1-RUNX1T1, 23/69 (33.3%) had two or more additional mutations. Most common were mutations (mut) in KIT (23/139; 16.5%), followed by NRAS (18/139; 12.9%) and ASXL1 (16/139; 11.5%). FLT3-ITD and mutations in FLT3-TKD, CBL, and KRAS were found in 4.3% - 5.0% of all pts, whereas mutations in IDH2 and JAK2 were detectable in 3.6% and 2.9%, respectively. IDH1 mutations were found in only 0.7% (1/139). NPM1mut and MLL-PTD were mutually exclusive of RUNX1-RUNX1T1. FLT3-ITD as well as FLT3-TKD were exclusive of ASXL1 mutations. With exception of FLT3-ITD, which was only present in de novo AML, there was no difference in mutation frequencies between de novo AML and t-AML.

69.8% (97/139) pts had at least one chromosomal aberration in addition to t(8;21)(q22;q22). Most frequent was the loss of either X- or Y-chromosome (together 46.8%), followed by del(9q) (15.1%), and trisomy 8 (5.8%). FLT3-ITD, FLT3-TKD and trisomy 8 were found to be mutually exclusive. The number of secondary chromosomal aberrations did not differ significantly between pts with de novo AML and t-AML, showing only a trend towards higher frequency of -Y, del(9q), and trisomy 8 in pts with t-AML.

Survival was calculated in pts who received intensive treatment (n=111/139, 79.9%; median follow-up 26.9 months; 2-year survival rate 73.4%). With exception of KITD816 mutation, which had a negative impact on overall survival in pts with de novo AML (2-year survival rate 64.2% vs. 82.3%, p=0.03), none of the other 13 mutations significantly influenced outcome, not even in case of 2 or more coexistent mutations. Also, no influence of additional chromosomal aberrations on survival was found.

In selected cases (n=21/139), we compared dynamic changes in the patterns of genetic lesions at diagnosis and at relapse. In 14/21 (66.7%) pts the initial molecular mutation pattern changed at relapse. Mutations commonly gained at relapse were KIT mutations (6/21, 28.6%), followed by ASXL1 and IDH1R132 (each 2/21, 9.5%). FLT3-ITD, CBL, NRAS and JAK2 mutations emerged in 1/21 patients (4.8%) each. Loss of a mutation at relapse has been observed in KIT, ASXL1, and NRAS (each 2/21, 9.5%), as well as in KRAS, FLT3-ITD and FLT3-TKD (each 1/21, 4.8%). Concerning chromosomal alterations at relapse, 7/21 pts (33.3%) showed a change of their initial cytogenetic pattern, mostly shifting to a more complex karyotype (gain of chromosomal aberrations: 5/21, 23.8%; loss of chromosomal aberrations: 2/21, 9.5%). In all cases, t(8;21)(q22;q22)/RUNX1-RUNX1T1 remained stable at time of relapse.

1) 50% of t(8;21)/RUNX1-RUNX1T1 positive pts had at least one additional molecular mutation and almost 70% showed additional chromosomal abnormalities. 2) KIT was the most frequent additional molecular mutation, followed by NRAS and ASXL1. 3) The only additional genetic marker with a significant adverse prognostic impact was KITD816 mutation.

Krauth:MLL Munich Leukemia Laboratory: Employment. Eder:MLL Munich Leukemia Laboratory: Employment. Alpermann:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.