Cheson and other members of the International Working Group (IWG) to Standardize Response Criteria reported criteria for a cytogenetic response following therapy of a patient with a myelodysplastic syndrome.


At least 20 metaphases are required to evaluate a patient for a cytogenetic abnormality. Fluorescent in situ hybridization (FISH) targeting a specific defect is an acceptable alternative.


Cytogenetic Abnormality

Number of Metaphases Required for Diagnosis

structural abnormality

>= 2

additional chromosome (trisomy)

>= 2

chromosomal loss (monosomy)

>= 3


The response to therapy is determined by comparing the cytogenetic findings before and after therapy.


Type of Response



disappearance of the abnormality

minor response (partial response)

>= 50% reduction of abnormal metaphases


Since a dysplastic cell may have multiple cytogenetic abnormality, each would need to be assessed for its response.


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