Clonal evolution with isodicentric Ph1 chromosome in Ph1-positive CML: karyotypic conversion after bone marrow transplantation.

Clonal chromosomal evolution was observed in a 16-year-old boy suffering from Ph1-positive CML. An isodicentric Ph1 chromosome appeared 20 weeks after the initial diagnosis. At that time an allogeneic bone marrow transplantation was performed. Thereafter, during an observation period of more than 13 months, chromosome analyses showed neither the Ph1 chromosome nor the abnormal isodicentric variant. Close cytogenetic monitoring is suggested to reveal early unfavorable prognostic signs of the onset of blast crisis before it becomes evident in the bone marrow morphology.