Influence of Hyperdiploidy on Ph 1 Prevalence Response to Therapy in Chronic Myelogenous Leukaemia

S ummary . In earlier investigations, evidence was found to suggest that hyperdiploid cells are less sensitive to cytostatic treatment than other Ph 1 ‐positive cells. The object of the present paper is to test this hypothesis. In a blood culture material, two treatment groups were defined according to the extent of the cytostatic therapy of the patients in the period preceding the time of sampling. The patients in treatment group T had received cytostatics for a total of 30 days or more during the preceding 2 months or had been treated continuously for the last 14 days. Group t originated from patients not fulfilling these demands. Each treatment group was subdivided into two Ph 1 prevalence classes, one with more and one with less than 50 per cent Ph 1 ‐positive cells. In group T, the average frequency of hyperdiploid Ph 1 ‐positive cells was found to be significantly higher in cultures with more than 50 percent Ph 1 ‐positive cells than in cultures with less. Group t did not show a corresponding difference. Closer analysis of group T revealed a linear positive correlation between the Ph 1 prevalences and the logarithms of the proportions of hyperdiploid Ph 1 ‐positive cells. The best explanation of these results seems to be that hyperdiploid cells are less sensitive to cytostatic treatment than other Ph 1 ‐positive cells. This assumption is in agreement with and supplements earlier results and seems to lead to the conclusion that development of high frequencies of hyperdiploid Ph 1 ‐positive cells involves haematological and clinical progression of chronic myelogenous leukaemia.