der(1;7)(q10;p10) is a recurrent chromosomal abnormality found in a wide variety of myeloid neoplasms observed in as high as 6% of myelodysplastic syndromes (MDS) in Asian populations, while rarely observed in Caucasian populations. It is thought to be generated by a recombination between two highly homologous centromere alphoid sequences which lead to an unbalanced abnormality of monosomy of 7q and trisomy of 1q. However, despite the presence of -7q, der(1;7) has been associated with a better prognosis compared to monosomy 7 or other del(7q) (-7/del(7q)). In addition to its association with +8 and del(20q), frequent RUNX1 mutations and a paucity of mutated TP53 have been reported in der(1;7) tumors, but otherwise, the molecular features of this abnormality have been poorly characterized in the literature. This is most likely because it is very rare in Caucasians, even though it represents one of the most prevalent lesions among Asian populations. The purpose of our study is to clarify the frequency and mutational landscape of der(1;7) in myeloid neoplasms on the basis of targeted-capture sequencing.

A total of 1,707 MDS cases, including 944 German and 763 Japanese cases, were enrolled, from which we identified 73 (4.0%) cases with der(1;7). The prevalence was >20 times higher in Japanese (9.0%) than German (0.43%) cohorts (p<0.0001). We also identified a strong male predominance in der(1;7)-positive cases (90.4%) compared to negative cases. Also including an additional 22 cases, somatic mutations and copy number abnormalities in der(1;7) were interrogated in a total of 95 cases, which included 84 (88.4%) with MDS, 9 (9.5%) with AML, and 2 (2.1%) with MPN. Among MDS patients, 29 were low-risk, 47 were high-risk, and the rest were not specified.

In mutation analysis, at least one mutation was detected in 98% of der(1;7) cases, most frequently affecting RUNX1 (42%), followed by EZH2 (26%), and ETNK1 (25%). Copy number analysis showed a high frequency of del(20q) and trisomy 8 in der(1;7) cases: 27.4% and 18.9% respectively. On the basis of mutant cell fractions, most of these mutations were present in subclones acquired within the major population harboring der(1;7). In particular, most of the EZH2 (7q35-q36) mutations were thought to be secondary events in der(1;7)-positive cases, while representing initial events acquired before UPD(7q) or -7/del(7q) in der(1;7)-negative cases. Of interest, der(1;7) was associated with a low frequency of TP53 mutations, which were seen only in 3% of cases with der(1;7), whereas highly prevalent in non-der(1;7) cases with -7/del(7q) (52%), which is concordant with a better clinical outcome was observed in der(1;7) cases compared with non-der(1;7) cases with monosomy 7 or other del(7q). Another unique feature of der(1;7) positive MDS was an extremely high frequency of RUNX1 mutations. However, the most prominent finding with secondary mutations in der(1;7) cases is the frequent hot spot mutation in ETNK1, which were originally reported in 8.8% of myeloid neoplasms with MPN features, like SETBP1 mutations. ENTK1 mutations were found in as many as 25% (23/95) of der(1;7) cases, while rarely seen in -7/del(7q) (1/89) (p<0.0001) or amp(1q) (2/68) (p=0.0001). Despite the high frequency of trisomy 8 observed in der(1;7) cases, none were associated with ETNK1 mutations. In addition, all of the RAS pathway mutations (positive in 16 cases) were observed in der(1;7) cases with wild-type ETNK1, while none were in ETNK1-mutant cases. Morphologically, these ETNK1-mutated der(1;7) cases presented with an increased eosinophil count in peripheral blood (760.9/ul vs. 78.1/ul) (p<0.001), compared to those without EKNK1 mutations, suggesting that ENTK1-mutated der(1;7) cases represent a novel disease entity within der(1;7), characterized by unique genetic features and increased eosinophils.

In conclusion, der(1;7) is a genetically and clinically distinct subset of myeloid neoplasms, which showed unique features that are distinct from MDS cases in -7 and other del(7q). Especially, ETNK1 mutations subdivided cases with der(1;7) into two groups of genetically distinct subsets as shown in Figure 1. In the future, inhibition of the kinase activity in ETNK1 could be a novel therapeutic strategy in such a previously unrecognized subset as characterized by der(1;7) and eosinophilia.

Disclosures

Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Baer:MLL Munich Leukemia Laboratory: Employment. Nadarajah:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Atsuta:Janssen Paharmaceutical K.K.: Honoraria; Mochida Pharmaceutical Co. Ltd: Honoraria; Kyowa Kirin Co., Ltd: Honoraria; Chugai Pharmaceutical Co., Ltd.: Honoraria. Handa:Ono: Research Funding. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Ogawa:Qiagen Corporation: Patents & Royalties; Kan Research Laboratory, Inc.: Consultancy; ChordiaTherapeutics, Inc.: Consultancy, Equity Ownership; Dainippon-Sumitomo Pharmaceutical, Inc.: Research Funding; Asahi Genomics: Equity Ownership; RegCell Corporation: Equity Ownership.

Author notes

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Asterisk with author names denotes non-ASH members.