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 (p170) by immunocytochemistry (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 MDR may contribute significantly to treatment failure.
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 (p170) by immunocytochemistry (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 MDR may contribute significantly to treatment failure.