Chromosome abnormalities after chlorambucil therapy of polycythaemia vera.

Bone marrow chromosomes were studied in 2 patients with polycythaemia vera (PV) at the time of diagnosis and several times subsequently during therapy with chlorambucil. Both patients were normal in the initial study, but later developed pathological diploid cell lines with structural chromosome abnormalities. Case 1 presented after 25 months of myelosuppressive therapy a deletion of chromosome no. 12, del (12) (p11), in 60% of the diploid cells. 10 months later all studied cells in the marrow contained this deletion. In addition, the deletion of chromosome no. 20, described as characteristic for PV, was found in 3 cells. Case 2 demonstrated after 40 months on chlorambucil the presence of a balanced translocation, t (1;5) (p36;q31) in 90% of the cells. In none of the patients were any definite clinical, laboratory or morphological signs of an approaching leukaemic transformation of the polycythaemic disorder present.