Overexpression of MDR-related p170 glycoprotein in chronic myeloid leukemia

Background and methods. Philadelphia (Ph) positive chronic myeloid leukemia (CML) cannot be induced into a true remission with conventional chemotherapy. Blast cells and precursors obtained from 51 Ph⁺ CML cases were assayed for expression of the multidrug resistance (MDR)-associated glycoprotein (p 170) by immunocytochemistty (APAAP) with the MRK-16 monoclonal antibody. Results and conclusions. Positive cells were found in 11/17 cases in chronic phase (65%), in 4/8 cases in accelerated phase, and in 23/26 cases in blastic phase (89%). The proportion of positive cells, which ranged between less than 1% and 95%, was higher in blastic phase (mean 32 ± 29.9) than in chronic phase (mean 3 ± 5.3) (p = 0.006). These findings show that p170 overexpression is common in Ph⁺ CML, especially after progression to blastic phase, and suggest that p170-related MDB may contribute significantly to treatment failure.