Acknowledgements
This work is supported by the European Commission (FP7, Fission-2011-295513 (RENEB) and NRBC-C2. TGS is a post- doctoral fellow from EUROTALENTS CEA-EC Cofund pro- gram. We acknowledge Dr. P. Venkatachalam, SRU, Chennai, and Dr. N.K. Chaudhury, INMAS, Delhi, for their input to improve the CBMN assay.
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Thomas S.K. Wan (ed.), Cancer Cytogenetics: Methods and Protocols, Methods in Molecular Biology, vol. 1541, DOI 10.1007/978-1-4939-6703-2_18, © Springer Science+Business Media LLC 2017
Chapter 18
Recurrent Cytogenetic Abnormalities in Myelodysplastic Syndromes
Meaghan Wall
Abstract
Cytogenetic analysis has an essential role in diagnosis, classifi cation, and prognosis of myelodysplastic syndromes (MDS). Some cytogenetic abnormalities are suffi ciently characteristic of MDS to be considered MDS defi ning in the appropriate clinical context. MDS with isolated del(5q) is the only molecularly defi ned MDS subtype. The genes responsible for many aspects of 5q- syndrome, the distinct clinical phenotype associated with this condition, have now been identifi ed. Cytogenetics forms the cornerstone of the most widely adopted prognostic scoring systems in MDS, the international prognostic scoring system (IPSS) and the revised international prognostic scoring system (IPPS-R). Cytogenetic parameters also have utility in chronic myelomonocytic leukemia (CMML) and have been incorporated into specifi c prognostic scoring systems for this condition. More recently, it has been appreciated that submicroscopic copy number changes and gene mutations play a signifi cant part in MDS pathogenesis. Integration of molecular genetics and cytogenetics holds much promise for improving clinical care and outcomes for patients with MDS.
Key words Myelodysplasia , Karyotype , Cytogenetics , Chronic myelomonocytic leukemia , Therapy- related myeloid neoplasms , IPSS-R , Diagnosis , Prognosis , SNP-A , Mutations
1 Introduction
Myelodysplastic syndromes (MDS) are a heterogeneous group of disorders characterized by clonal and ineffective hematopoiesis.
Ineffective blood production manifests morphologically as dyspla- sia and leads to one or more cytopenias. The blast count may be normal or elevated but is less than 20 % in the bone marrow and peripheral blood . There is a heightened risk of progression to acute leukemia. Therapy- related cases are set apart from de novo MDS by a history of exposure to DNA-damaging agents. Chronic myelo- monocytic leukemia (CMML) shares the dysplastic morphologic changes and leukemia risk found in MDS. However, it is distin- guished by evidence of myeloproliferation in the form of a periph- eral blood monocytosis, which may be accompanied by leucocytosis and neutrophilia, and it is therefore categorized as a myelodysplas- tic/myeloproliferative syndrome.
MDS and CMML are predominantly disorders of aging with a median age at diagnosis of 73–77 years [ 1 , 2 ]. X chromosome inactivation studies [ 3 ], and more recent studies using massively parallel sequencing techniques, have shown that a signifi cant pro- portion of older people have evidence of clonal hematopoiesis without compromise of blood production suffi cient for diagnosis of a myeloid malignancy [ 4 , 5 ]. This condition has been labeled clonal hematopoiesis of indeterminate potential ( CHIP ) [ 6 ].
CHIP carries a risk of approximately 1 % per year of developing a hematological malignancy, analogous to the risk of plasma cell myeloma in monoclonal gammopathy of uncertain signifi cance.
Metaphase cytogenetics identifi es abnormalities in approxi- mately 50 % of MDS cases and 30 % of CMML cases. Cytogenetic abnormalities have broad-ranging clinical utility with implications for diagnosis and prognosis. MDS with isolated del(5q) is known to be a lenalidomide-responsive condition with a clearly elucidated molecular mechanism. Integration of additional genomic informa- tion, provided by DNA microarrays and sequencing, holds great promise in further refi ning the classifi cation and management of these disorders.
2 Diagnosis and Classifi cation of MDS and CMML
Cytogenetic abnormalities are present in 35–50 % of de novo MDS cases [ 2 , 7 – 9 ]. The World Health Organization (WHO) classifi ca- tion of tumors of hematopoietic tumors and lymphoid tissue rec- ognizes six categories of MDS: refractory cytopenia with unilineage dysplasia (RCUD), refractory anemia with ring sideroblasts (RARS), refractory cytopenia with multilineage dysplasia ( RCMD ), refractory anemia with excess blasts (RAEB), MDS with isolated deletion of 5q and MDS unclassifi able (MDS- U ) [ 10 ]. MDS with unilineage dysplasia ( RCUD and RARS subtypes) tend have more favorable outcomes than RCMD and then RAEB in turn, and cytogenetic abnormality rates vary accordingly. Abnormalities are identifi ed by metaphase cytogenetics in approximately 11–34 , 32–43, 46, and 50–59 % cases of RARS, RCUD, RCMD, and RAEB, respectively [ 7 , 8 ].
By defi nition, according to the 2008 version of the WHO clas- sifi cation, del( 5q ) is present as a sole abnormality in all cases of MDS with isolated deletion of 5q and so the abnormality rate is 100 % in this subtype. In recent years, data have emerged indicat- ing that del(5q) cases with one additional abnormality, other than
−7 or del(7q) , have equivalent clinical outcomes to cases where del(5q) is present as the sole abnormality [ 9 , 11 , 12 ]. Therefore, the 2016 revision of the WHO classifi cation will allow cases with del(5q) plus one other abnormality to be categorized as MDS with isolated del(5q), providing the second abnormality is not del(7q)
or −7 [ 13 ]. MDS with isolated del(5q) is the only molecularly defi ned MDS category and 5q- syndrome is the best understood contiguous gene syndrome in MDS. It has been shown that mac- rocytic anemia is the result of haploinsuffi ciency for the RPS14 gene at 5q33 [ 14 ] and deletion of nearby microRNA clusters are responsible for the hypolobated megakaryocyte phenotype [ 15 ].
Haploinsuffi ciency of a third gene, CSNK1A1 is required for lenalidomide sensitivity [ 16 ].
In contrast to acute myeloid leukemia (AML) where balanced abnormalities predominate, unbalanced abnormalities are more common in MDS. Overall, the most frequent abnormalities are loss of the Y chromosome (-Y), del(5q) , +8, del(20q), and −7 [ 2 , 7 – 9 ]. Assessment of morphologic dysplasia in cases of possible MDS can be challenging and is subject to signifi cant interobserver variability [ 17 ]. In the setting of persistent cytopenia where mor- phologic criteria for a diagnosis of MDS have not been met, the WHO classifi cation considers some cytogenetic abnormalities suf- fi ciently characteristic of this condition to be MDS defi ning [ 10 ].
Cases that qualify for an MDS diagnosis by virtue of a characteristic cytogenetic abnormality fall into the MDS-U category. Unbalanced abnormalities considered presumptive evidence of MDS include
−5, del(5q) , −7, del(7q), del(9q), del(11q), del(12p) or transloca- tions involving 12p, − 13 or del(13q), i(17q) or translocations involving 17p, and the isodicentric Xq (Fig. 1 ). These abnormali- ties occur in MDS with estimated frequencies between 1 and 10 %.
Balanced abnormalities are more unusual in MDS. None occur with a frequency of more than 1 %. However, the t(1;3)(p36.1: q26) , t(2;11)(p21;q23) , t(6;9)(p22;q34), and inv(3)(q21q26) recur with suffi cient frequency to be considered MDS defi ning. Notably,
Fig. 1 Partial G- banded karyotypes of unbalanced, structural abnormalities con- sidered presumptive evidence of MDS. In each panel the abnormal chromosome is shown on the right with the normal chromosome on the left for comparison. ( a ) del(5)(q12q34), ( b ) del(7)(q22q36), ( c ) del(9)(q22q33), ( d ) del(11)(q14q23) , ( e ) del(12)(p12p13) , ( f ) del(13)(q12q14), ( g ) i(17)(q10), ( h ) idic(X)(q13)
detection of MDS-defi ning abnormalities by fl uorescence in situ hybridization (FISH) or other molecular techniques is not consid- ered presumptive evidence of MDS. To be MDS defi ning, abnor- malities must be identifi ed by conventional karyotyping [ 13 ]. Loss of the Y chromosome, although common in men with MDS, may be observed as an age-related phenomenon in the absence of a hematological disorder and so cannot be considered presumptive evidence of MDS. Trisomy 8 and del(20q) are also common in MDS , but are not suffi ciently specifi c to this disorder. Consequently, they are also excluded from the list of MDS-defi ning cytogenetic abnormalities.