Should additional testing be done if bone marrow aspiration indicates myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML)?

Additional Testing After Bone Marrow Aspiration Showing MDS or AML

Yes, comprehensive additional testing is mandatory when bone marrow aspiration indicates either MDS or AML, as morphology alone is insufficient for complete diagnosis, risk stratification, and treatment planning.

Essential Testing for Both MDS and AML

Cytogenetic Analysis (Highest Priority)

• Standard karyotyping of 20-25 metaphases is mandatory for all suspected myeloid neoplasms, as cytogenetic abnormalities have the highest prognostic weight in both MDS (IPSS-R) and AML 1.
• If fewer than 10 analyzable metaphases are obtained, FISH analysis must be performed for critical abnormalities including monosomy 5/del(5q), monosomy 7/del(7q), trisomy 8, TP53 deletion, and del(20q) 1.
• Cytogenetic analysis should use at least two different cell cultures (24h and 48h) with documentation according to International System for Human Cytogenetic Nomenclature (ISCN) 1.

Immunophenotyping

• Flow cytometry with comprehensive myeloid, monocytic, and lymphoid antibody panels is required to determine lineage, distinguish AML from acute lymphoblastic leukemia, and identify mixed phenotype acute leukemias 1.
• Essential markers include MPO, CD13, CD33, CD117, CD34, HLA-DR for myeloid lineage assignment 1, 2.
• This is particularly critical for classifying FAB M0 (MPO-negative by cytochemistry but positive by immunophenotyping) and M7 (CD41/CD61-positive) subtypes 1.

Molecular Genetic Testing

• Next-generation sequencing panels for recurrent mutations are strongly recommended in both MDS and AML 1.
• Priority genes include:
  • Epigenetic regulators: TET2 (15-25%), ASXL1 (10-20%), DNMT3A (10%), IDH1/2 (5-10%) 1
  • Splicing factors: SF3B1 (15-30%), SRSF2 (10-15%), U2AF1 (5-10%) 1
  • Transcription factors: RUNX1 (10-15%), TP53 (5-10%) 1
  • Signaling molecules: NRAS/KRAS (10%) 1
• TP53 mutation analysis is particularly important in patients with del(5q) MDS who show poor response to lenalidomide, as mutations cause treatment resistance 1.

Additional Testing Specific to AML

Bone Marrow Trephine Biopsy

• Bone marrow biopsy is required in addition to aspirate when there is a dry tap, suspected underlying MDS, or need to assess cellularity and fibrosis 1.
• CD34 immunohistochemistry on biopsy sections is invaluable when marrow is hypocellular, fibrotic, or yields inadequate aspirate for accurate blast enumeration 2.

CNS Evaluation (Pediatric AML)

• Cerebrospinal fluid examination is mandatory in all pediatric AML patients at diagnosis to detect CNS involvement, defined as >5×10⁶/L WBCs with blasts in non-bloody tap 1.
• Lumbar puncture should be postponed in patients with severe thrombocytopenia, coagulopathy, or acute promyelocytic leukemia until bleeding risk is controlled 1.

Additional Testing Specific to MDS

Bone Marrow Biopsy

• Trephine biopsy is strongly recommended at diagnosis to assess cellularity, fibrosis, and megakaryocyte dysplasia, and to diagnose hypoplastic or fibrotic MDS variants 1.
• Biopsy is essential when aspirate is hypocellular, shows dry tap, or when differential diagnosis includes aplastic anemia 1.

SNP Array Analysis

• SNP array should be performed when standard karyotype is normal or yields insufficient metaphases, as acquired copy-neutral loss of heterozygosity (aCN-LOH) occurs in regions harboring poor-prognosis mutations (ASXL1, EZH2, TP53, RUNX1) 1.
• This is particularly important for detecting submicroscopic abnormalities that provide prognostic information for IPSS-R scoring 1.

Critical Diagnostic Pitfalls

• Blast enumeration requires a 500-cell differential count on bone marrow aspirate to ensure diagnostic accuracy, as the 20% blast threshold distinguishing MDS from AML has critical therapeutic implications 2, 3.
• Hemodilution of specimens can falsely lower blast percentages in flow cytometry, particularly in fatty or fibrotic marrows; morphological inspection must never be replaced by flow results alone 1.
• Cytogenetic failures are common in markedly hypocellular marrows (<10% cellularity); peripheral blood FISH for chromosomes 5 and 7 abnormalities can serve as quality control 1.
• In cases with normal karyotype and minimal dysplasia, molecular testing demonstrating MDS-associated mutations can establish clonal disease and distinguish from idiopathic cytopenias of uncertain significance (ICUS) or idiopathic dysplasia of unknown significance (IDUS) 1.

Rationale for Comprehensive Testing

The distinction between high-risk MDS and AML represents a continuum of the same disease process, with shared genetic abnormalities carrying crucial prognostic implications 4. Treatment decisions—including intensity of chemotherapy, eligibility for targeted therapies (FLT3 inhibitors, IDH inhibitors, venetoclax combinations), and allogeneic stem cell transplantation candidacy—depend entirely on complete molecular and cytogenetic characterization 5, 4. Morphology and blast percentage alone are insufficient for optimal risk stratification and treatment selection in modern hematologic practice 5, 6.