1. Clinical and Histologic Evaluation of Myelodysplastic Syndromes

2. Myelodysplastic syndromes (MDS) are several clonal hematologic disorders characterized by ineffective and disorderly hematopoiesis. The hallmarks of MDS include peripheral blood cytopenias (95% of patients are anemic at diagnosis, whereas 35-50% have neutropenia or thrombocytopenia, or both), dysplastic changes, and a risk of progression to higher-risk forms of MDS and to acute myeloid leukemia (AML).[1] AML is diagnosed when the blast count (bone marrow or peripheral blood) is 20% or higher (with a few exceptions).[1] Approximately 50% of patients have a clonal cytogenetic abnormality detectable with routine GTG-banded karyotyping.[1] However, even patients with a normal karyotype commonly demonstrate somatic point mutations (ie, evidence of clonal hematopoiesis).

3. MDS are diseases of aging; the risk of the disorder increases as mutations occur throughout the life span in hematopoietic stem and progenitor cells. The median age at diagnosis is approximately 70 to 75 years, and MDS are rare before age 50, except in patients with therapy-related MDS who have been treated with alkylating agents, topoisomerase inhibitors, or radiotherapy for another condition (eg, breast cancer or systemic lupus erythematosus).[1,2] In patients who are diagnosed with MDS at a young age without such a history, Fanconi anemia must be ruled out, because therapeutic protocols differ for patients with MDS secondary to Fanconi anemia. Other causes of familial MDS include germline mutations in RUNX1 and GATA2 genes. The incidence of MDS has been difficult to establish because many elderly patients with cytopenias are incompletely evaluated, especially if they have serious comorbid conditions.[2,3]

4. “All that is dysplastic is not MDS
“All that is dysplastic is not MDS.” Other causes of dysplasia, such as nutritional deficiency or toxin exposure, must be ruled out, especially when morphologic and cytogenetic evaluation reveals a normal karyotype and no excess blasts.[1] Communication between the pathologist and the referring clinician, and correlation with the clinical picture, is critical to ensure the most appropriate evaluation is undertaken.[2]

5. These evaluations are helpful in the initial work-up of most cases of MDS, in order to exclude common nutritional or toxic causes of cytopenias.

6. In some cases, the presentation of MDS is atypical and the diagnosis may be difficult to make.[1] On the other hand, other neoplastic conditions may mimic the signs and symptoms of MDS. Therefore, bone marrow examination is essential when MDS are within the differential and initial blood tests are unrevealing. Although this table is not exhaustive, these are some other disorders that overlap clinically and/or morphologically with MDS. Again, communication between the pathologist and the referring clinician, and correlation with the clinical picture, is key.

7. This slide continues the list of other disorders which overlap clinically and/or morphologically with MDS and make diagnosis difficult.

8. In some patients with cytopenias or with occasional dysplastic cells, it is not possible to make the diagnosis of MDS securely at the time of initial evaluation. While minimal diagnostic criteria for MDS are debated, evidence of clonality is now considered critical to making the diagnosis. In the absence of excess blasts or a clonal karyotypic marker, dysplasia must be extensive and other causes of dysplasia, such as nutritional deficiencies, need to be ruled out. For patients for whom MDS can not yet be diagnosed, the term Idiopathic Cytopenia(s) of Undetermined Significance (ICUS) has been proposed. Such patients are at risk for MDS and AML evolution and should be followed closely.[4,5]

9. The most recent publication of the WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues (2008) classifies adult MDS into 7 categories on the basis of clinical features, including: cytopenia(s); morphologic features (dysplasia, blast count, presence of ring sideroblasts); and in some cases the presence of certain cytogenetic abnormalities.[1] This classification system, which is shown on this slide and the next one, provides pathologists with criteria for diagnosis, and also affords some information for stratifying risk. Categories with multilineage dysplasia and excess blasts are considered to be at higher risk for progression. MDS-U has a variable course.

10. This slide shows the rest of the MDS classification system from the WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues (2008).

11. In general, the thresholds for cytopenias are: hemoglobin <10 g/dL, neutrophil count <1,800/μL and platelet count <100,000/μL.[1] However, the diagnosis of MDS may still be made in the absence of cytopenias if definitive histologic and/or cytogenetic features are present. The most common finding is anemia, often characterized by a macrocytosis (MCV greater than 100μm3). Dysplastic changes in the myeloid lineage may be present. Evaluation for circulating blasts is important, as the MDS classification will vary if the circulating blast count is less than 1%, 1%, 2-4%, or 5-19%. A circulating myeloid blast count of 20% or greater is diagnostic of acute myeloid leukemia.

12. The bone marrow examination is a multi-part process including removal of a core of intact marrow as well as multiple aspirate pulls.[1,2] A well-prepared, well-stained aspirate smear is absolutely essential to allow for accurate assessment of dysplasia (particularly erythroid and myeloid), evaluation of blasts, and assessment for the presence of Auer rods. A minimum of 200 erythroid, 200 myeloid, and 30 megakaryocytic elements should be assessed, which is generally accomplished by counting 500 cells. Often megakaryocytic dysplasia is best evaluated on the core biopsy sections. The core biopsy also permits for evaluation of cellularity (typically hypercellular; uncommonly hypocellular) and fibrosis (typically none to minimal; uncommonly increased).

13. Dysplastic changes within the erythroid lineage include: abnormal nuclear contours (such as budding), megaloblastoid changes manifested as nuclear:cytoplasmic dyssynchrony, multinucleation (especially unequal nuclear sizes), internuclear chromatin bridging, karyorrhexis, ring sideroblasts, and the presence of poorly-defined vacuoles in the cytoplasm. Ring sideroblasts are defined red cell precursors with 5 or more iron granules encircling one-third or more of the nucleus. Using a periodic acid-Schiff cytochemical stain, the cytoplasmic vacuoles may demonstrate positivity (pink staining) in a granular or diffuse pattern. A given case may show one or more of these features.

14. Dysplastic changes within the myeloid lineage include: nuclear hypolobation/hyposegmentation (pseudo Pelger-Huët forms), nuclear hypersegmentation, hypercondensed/clumped chromatin, cytoplasmic hypogranularity, and the presence of large, abnormal Chediak-Higashi-like granules in the cytoplasm. Small cell size may also be seen. A type of pseudo Pelger-Huët form in which two nuclear lobes are connected by a thin strand of cytoplasm is referred to as a ‘pince-nez’ form, but monolobated neutrophils also fall under the designation of pseudo Pelger-Huët. A given case may show one or more of these features.

15. Dysplastic changes within the megakaryocytic lineage include: micromegakaryocytes ( 15μm), hypolobated megakaryocytes (any size), and megakaryocytes with multiple nuclei that are separated or widely-spaced. A particular type of dysplastic megakaryocyte with 3 separated nuclear lobes is known informally as a “pawn ball” megakaryocyte because of its resemblance to the historic symbol of pawnbroking (three separate balls or orbs displayed on a sign outside of a pawnbroker’s shop). Although a given case may show one or more of these features, the dysplasia observed in MDS with isolated del(5q) is predominantly comprised of normal or increased numbers of megakaryocytes with hypolobated/non-lobated nuclei.

16. Accurate assessment of the blast count is a vital step in MDS classification. In the peripheral blood, MDS classification will vary if the circulating blast count is less than 1%, 1%, 2-4%, or 5-19%. Review of a well-prepared bone marrow aspirate smear (500-cell count) not only provides a blast count but also permits evaluation for Auer rods. In both the blood and the bone marrow, the presence of Auer rods classifies the process as RAEB-2 when the blast count is 1-19%. CD34 immunohistochemistry performed on the bone marrow will often mark blast forms (thereby facilitating estimation of percent involvement) and will also highlight aberrant architectural features such as clusters and aggregates of immature forms away from where they are normally found, i.e. bone trabeculae and vasculature. CD34 also highlights blood vessels and may mark dysplastic megakaryocytes. Flow cytometric analysis may underestimate the blast count and should be used primarily for immunophenotyping (confirmation of CD34 expression; characterization of aberrant immunophenotypes).

17. Cytogenetic analysis of the bone marrow should be performed in every case of suspected MDS.[2] The initial investigation is by conventional cytogenetic analysis (CCA) of GTG-banded metaphases. If 20 high-quality metaphases are evaluated and show no abnormality, then an additional MDS-directed FISH panel does not need to be performed in cases of de novo MDS (low-yield). However, MDS-directed FISH panels should be performed to confirm any abnormalities detected by CCA, or if the obtained metaphases are < 20 or of poor quality. Accurate recognition of cytogenetic aberrations is critical for diagnosis and prognosis, and can also direct therapy (e.g. administration of lenalidomide in 5q- syndrome).

18. In cases of unexplained, persistent cytopenia(s), all abnormalities except trisomy 8, del(20q) and monosomy Y can be used as presumptive evidence of MDS in the absence of diagnostic morphologic features (MDS-U).[1] Monosomy Y is also a common normal finding in older men (though typically in less than 75% of examined metaphases). Therapy-related MDS, which has a higher rate of cytogenetic abnormalities than de novo MDS, frequently demonstrates complex karyotypes and most commonly demonstrates monosomy 7/del(7q) and/or monosomy 5/del(5q) (and, less frequently, t(11;16)(q23;p13.3) and/or t(3;21)(q26.2;q22.1)).

19. Certain genetic abnormalities define a case as acute myeloid leukemia, regardless of the blast count.[1]

20. Flow cytometric analysis of maturation patterns in hematopoietic elements has been proposed as an additional tool for dysplasia assessment, particularly in cases of suspected MDS where morphologic findings are subtle and cytogenetic analysis is unrevealing. Aberrant patterns of granulocyte, erythroid, and monocyte maturation may be observed. Currently, flow cytometric analysis is not part of diagnostic criteria and rather is used as supplementary information. In cases of suspected MDS with indefinite morphologic and cytogenetic features, the presence of  3 aberrant expression patterns (erythroid, granulocytic, or monocytic maturation) should prompt close clinical follow-up and reevaluation for more definitive features within several months.[1]

21. More than 25 recurrent mutations have been described in MDS, and more than 80% of cases have at least one of these mutations. In some instances the presence of a mutation (e.g., EZH2) provides additional prognostic information beyond what is available from clinical-pathological risk assessment tools. Testing for these mutations will increasingly be incorporated into evaluation of patients with suspected MDS.[2]

22. More than 25 MDS-associated mutations have been described, involving genes encoding proteins important for epigenetic patterning, pre-mRNA splicing, cell proliferation, cell differentiation, and DNA repair, as well as several genes encoding proteins of unknown function. None of these are present in more than 25% of patients, though individual mutations such as SF3B1 may be associated with a specific morphology (>70% of RARS patients have SF3B1 mutations, most commonly K700E). The size of the circle in this figure is proportional to the frequency with which the specific gene is found to be mutated in MDS.[7]

23. Since the natural history of MDS varies so widely, and this influences clinical management, several clinical risk stratification schemes have been developed to help predict the clinical course.[8-11] These include the IPSS, IPSS-R, WPSS, and MD Anderson Risk Model. Although none of these systems are perfect – for instance, none account for comorbid conditions or for the pace of disease, and only the MD Anderson system has been validated in previously treated patients and those with secondary/therapy-related MDS – they are useful guidelines.

24. The 2012 IPSS-R includes 5 karyotype risk groups
The 2012 IPSS-R includes 5 karyotype risk groups.[9] These have major implications for prognosis. Cytogenetics are the most heavily weighted factor in the IPSS-R, given even greater weight than blast proportion.

25. The IPSS-R adds together scores from 5 parameters – karyotype, blast proportion, and 3 cytopenias - to obtain a summed score.[9]

26. The IPSS-R includes 5 risk groups, with a median survival of almost a decade in the lowest risk group to less than a year in the highest (“very high”) risk cohort. More than 25% of patients had their risk assessment changed between IPSS and IPSS-R.

28. Abbreviations

29. Abbreviations (cont)

30. References

31. References (cont)

32. References (cont)