Chromosomal abnormalities in acute promyelocytic leukaemia.

In 2 patients with acute promyelocytic leukaemia (APL) an isochromosome for the long arm of chromosome 17 was seen in part of the bone marrow mitoses at diagnosis and relapse, respectively. In one of them, there was a t(15q+; 17q-) affecting one of the No. 15 chromosomes and both arms of the isochromosome. Thus the translocations must have occurred before (or simultaneously with) the formation of the isochromosome. This is the first example of t(15;17) out of 17 patients with APL studied in Finland.