Chromosome banding studies in Philadelphia chromosome positive myeloid leukaemia.

A cytogenetic study of Ph1 positive myeloid leukaemia in both chronic and acute phases had been made by a chromosome banding technique. The translocation (t(9;22)(q34;q11), designated t(Ph1) was present in the myeloid cells of 43 of 44 patients; the exceptional case had normal number 9 chromosomes and a different translocation (t(19;22)(q13;q11)). A translocation additional to that involving the Ph1 was found as a stable abnormality present in all myeloid cells in 4 patients, chromosome 17 being involved in 2. The association of isochromosome number 17 with blast crisis was confirmed. New data were obtained concerning the significance of duplicated or dicentric Ph1 chromosomes and their relationship with the 9q+ anomaly. Monoclonal origin of Ph1 was confirmed in cases with polymorphic number 22 or 9 chromosomes.