Canterbury DHB

Diagnosis

It is important to distinguish reactive causes of cytopenias and dysplasia from primary bone marrow dysfunction i.e. myelodysplasia. This begins with a good clinical history specifically looking for previous exposure to chemotherapy, radiotherapy, immunotherapy, and occupational or other exposure to potential causative agents e.g. benzenes. A full medical, medication, and social history is required because the majority of patients with MDS are elderly. Specific follow-up investigations are dictated by the history.

The blood film and a bone marrow examination are the important investigations to establish a diagnosis (see the WHO classification for specific criteria). Cytogenetics should be tested in all cases because this forms an important part of the prognostic scoring system. The gold standard is a composite report which includes blood film, bone marrow aspirate and trephine, flow cytometry, and genetic testing.

Bone marrow aspirate

Standard MGG or Wrights stain and iron stain. If the sample is aparticulate, it may not be possible to make the diagnosis based on the aspirate alone.

Bone marrow trephine

Standard H+E and reticulin stain.

Immunohistochemistry

• In cases where the aspirate morphology is not clear cut, immunohistochemistry on the trephine sample can be helpful to confirm the diagnosis of MDS.
• CD34 can be used to assess the percentage of immature precursors and look for abnormally localised immature precursors (ALIPS) – immature precursors found in the interstitium rather than paratrabecular. If CD34 is negative on flow cytometry, CD117 or CD33 can be used.
• Glycophorin A or CD71 can be used to highlight and quantify the erythroid series in addition to looking for disrupted erythroid islands.
• CD61 or CD42b is useful to look for micromegakarocytes, abnormal localisation of megakaryocytes in the paratrabecular region, and clustering.

Flow cytometry

• Flow cytometry (FCM) can be used to identify aberrant antigen expression, which is indicative of dysplasia and should be used in the routine diagnosis of myelodysplasia. It is particularly helpful in cases where the morphological features of dysplasia are not clear cut and the cytogenetics are normal.
• A specific panel is currently being worked on in Christchurch and should be available in early 2020.
• The European LeukaemiaNet group have published guidelines on the use of flow cytometry in MDS. Four parameters are considered:
  1. The percentage of CD34+ precursors in the bone marrow.
  2. The frequency of B-cell precursors in the CD34+ subset.
  3. CD45 expression on myeloid progenitors in comparison to lymphocytes.
  4. Side scatter of granulocytes in comparison to lymphocytes.
• A high score is more suggestive of MDS, although high scores can be seen in reactive states. The reported sensitivity of FCM in MDS is between 59-98% and specificity 93-100%; however, this modality should be used in conjunction with the standard morphology (aspirate and trephine) and genetic testing.
• An increased number of abnormalities found on FCM is associated with a poorer outcome and higher risk of transformation to AML.
• In cases where the morphological features of dysplasia are minimal, aberrant FCM may support the diagnosis of MDS and abnormalities in more than one lineage may suggest multilineage dysplasia which will impact on the prognosis.
• If the FCM is normal and the morphological findings are minimal, re-evaluate the diagnosis carefully.
• Use immunophentyping in CMML to differentiate monocytes from monoblasts.

Genetics

• A patient’s genetic profile will critically impact on the clinical phenotype, prognosis and response to therapy.
• 50% of MDS cases have a cytogenetic abnormality, the majority of which are unbalanced, resulting in copy number abnormalities (CNAs), i.e. deletions or gains.
• The most common chromosomes affected are del(7q), del(5q), +8, del(20q).
• Many of these changes occur as part of a complex karyotype (>3 abnormalities) and 40-50% of these cases are associated with TP53 mutation particularly if del(5q) or del(17p) are involved.
• 2-3% have recurrent reciprocal translocations, which have a high diagnostic value even in the absence of morphological changes – t(3;21), inv(3), t(3;3), t(1;3), t(6;9).
• Patients with MDS carry a median of 9 somatic mutations and this includes both driver and passenger mutations.
• If you combine copy number abnormalities and somatic mutations, more than 78-90% of patients with MDS have ≥1 recurrent genetic abnormality.

Genotype-phenotype correlation

• The number of driver mutations significantly correlates with survival.
• Particular driver mutations are associated with a specific subtype of disease and predict for outcome independent of IPSS or R-IPSS. For example, SF3B1 mutations are strongly associated with ringed-sideroblasts and predict a favourable prognosis.
• With access to testing if SF3B1 is positive, >5% RS is diagnostic of MDS-RS.
• MDS/MPN-RS and thrombocytosis often have JAK2 mutation (or CALR/MPL).
• TP53 mutations are found in:
  • 25% high risk MDS
  • 10% primary AML
  • 50% therapy-related MDS/AML.
• 90% TP53 mutated patients have a complex karyotype.
• The strong negative impact of TP53-mutated patients cannot be overcome, even with alloSCT.
• Genetic testing in Christchurch is currently based on standard cytogenetics. However there is a role for single nucleotide polymorphism (SNP) arrays and next generation sequencing in the future.

Reference

Ogawa S. Genetics of MDS. Blood 2019 133; 10: 1049

Summary of the WHO Categories of Myelodysplasia

• See WHO classification (2016): Table 15. PB and BM findings and cytogenics of MDS (page 10)
• Arber, D. A., et al. (2016). The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood 127(20): 2391-2405.
• Killick, S. B., et al. (2014). Guidelines for the diagnosis and management of adult myelodysplastic syndromes. Br J Haematol 164(4): 503-525.

Summary of the WHO Categories of Myelodysplastic/Myeloproliferative Diseases

See WHO classification (2016): Table 11. Diagnostic criteria for CMML (page 8)

CMML

CMML is a disorder with features of both myeloproliferation and myelodysplasia. The median age at presentation is 76 years and it is associated with a short median survival of 20 months (range 7-60). The aggressive nature of the disease and the fact that most patients are older with comorbidities mean that it is difficult to treat.

A proportion of patients have more indolent disease with a low level peripheral blood monocytosis which simply needs to be monitored.

Indications for treatment:

• systemic symptoms
• organ involvement e.g. skin, splenomegaly, pulmonary infiltrates
• altered blood counts e.g. leucocytosis, cytopenias, and increased blast count

Treatment options include:

• Supportive care
• Hydroxyurea for proliferative cases to control counts or symptomatic splenomegaly
• Azacitidine for non-proliferative cases of CMML 2

Allogeneic stem cell transplantation is only available to a limited number of patients with CMML but should be considered in younger patients and those with poor risk disease who have a low comorbidity index. Patients may require intensive AML-type chemotherapy prior to proceeding with transplantation.

CMML can be divided into a proliferative type, generally WBC >13 x 10⁹/L and a dysplastic type, WBC <13 x 10⁹/L. In general the proliferative type has a worse outcome. The percentage of blasts also has a clear prognostic significance and it is important that the promonocytes are counted as blasts and separated from the mature monocytes in the cell differential. Perform flow cytometry because it helps distinguish the cell types.

Sub-types of CMML

⁺ If Auer rods are present in the blasts, classification is CMML-2.

Diagnostic criteria for the other main subtypes of MDS/MPN can be found in the following links. This includes atypical CML (aCML), MDS/MPN with ring sideroblasts and thrombocytosis and juvenile myelomonocytic leukaemia. The SETBP1 mutation can be found in up to one third of cases of aCML.

Atypical CML

This is a challenging disorder to diagnose and treat due to its presentation in older adults and aggressive course with high rates of transformation to AML. The following article provides a good summary of treatment options.

Gotlib, J. (2017). "How I treat atypical chronic myeloid leukemia." Blood 129(7): 838-845.

MDS/MPN with ringed sideroblasts and thrombocytosis

A new entity in the 2016 WHO classification of MDS/MPN which replaces "Refractory anaemia with ringed sideroblasts and thrombocytosis".

Treatment:

• In general these patients do not respond well to erythropoietin.
• They may respond to azacitidine if they are eligible for treatment.
• Ruxolitinib has also been shown to be effective, but it is not routinely available in New Zealand.
• Patients who are transfusion dependent respond well to lenalidomide. An NPPA is required for this.

See:

• WHO classification (2016): Table 12. Diagnostic criteria for aCML, BCR-ABL1 (page 8)
• WHO classification (2016): Table 13. Diagnostic criteria for MDS/MPN with ring sideroblasts and thrombocytosis and Table 14. Diagnostic criteria for JMML (page 9)

Topic Code: 4953