Chromosome Aberration following Radiophosphorus Treatment of Polycythaemia

Summary Cytogenetic examination was made of 51 polycythaemic patients. A total of 79 separate chromosome studies were made. Fifty‐six were from patients treated with radiophosphorus and 18 from patients treated by venesection only. Nine examinations were made of bone marrow and the remainder of leucocyte cultures. Accumulated doses of radiophosphorus were in the range 3‐2‐32‐5 mCi. The variation in all types of cytogenetic damage in the first two months after administration of the isotope did not allow early recognition of trends in dose response. After this period an increase in breaks, and possibly all rearrangements, could be recognized. Multiple regression analysis showed that the Cu type of chromosome damage is likely to be the most reliable index of absorbed dose. These in‐vivo studies show that small radiation dose increments of the order of several mCi 32 P are detectable in radiation‐treated pdycythaemics by an increase in the yield of dicentrics and rings as compared with untreated polycythaemics. Lymphopoietic stem cells may retain B type damage for periods longer than 20 half‐lives of radiophosphorus. Changes similar to those induced by radiation were seen in a small number of cases treated by radiw mimetic therapy. Aneuploidy was a consistent finding in the treated cases. Two clearlydefined hypomodal clones with the absence of one or two C group chromosomes were seen in the only case of acute leukaemia in the series. This paticnt had received 28.5 mCi 32 SP. Cytogenetic damage was randomly distributed throughout the chromosome groups of all patients.