P-glycoprotein (PgP), a transmembrane protein, has been associated with multiple drug resistance. We examined 42 patients with chronic lymphocytic leukemia immunohistochemically using the monoclonal antibody JSB-1 to determine the prevalence of PgP expression and its relationship with chemotherapy exposure. Of the 42 patients, 31 (74%) had detectable PgP. No relationship was found between PgP expression, patient age, duration of disease or stage. Moderate and strong intensity staining was found in 22% of untreated patients versus 56% patients treated with chemotherapy (p<0.05). Temporal fluctuations in P-glycoprotein staining intensity was seen in 6 of 7 cases which paralleled the initiation or withdrawal of the therapy.

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