Chemotherapy has proven to be effective in the management of high grade non-Hodgkin's lymphoma (NHL). However drug resistance remains a major clinical obstacle to effective disease control. One such well documented system involves multidrug resistance (MDR), characterized by the overexpression of a 170 kDa membrane protein termed P-glycoprotein (Pgp). Analysis of P-glycoprotein was done on lymph node biopsies obtained from 109 patients with high grade NHL. Patients were followed up for time periods ranging from 7 to 26 months after chemotherapy or until recurrent/residual disease was diagnosed. Analysis of Pgp in tissue samples was carried out by immunocytochemistry and Western blot. Of the 109 patients, 36 had either residual or recurrent disease. All these patients had a second lymph node biopsy done which was also analyzed for Pgp. P-glycoprotein was detected by immunocytochemistry in only 5 of the 73 patients who remained disease-free, while it was expressed in 26 of the 36 patients with residual/recurrent disease. All the 36 tissue samples of the latter group and 42 of the 73 biopsies of the disease-free group were re-analyzed by Western blot. Only one of the 42 samples from the disease-free group showed a positive Western blot reaction while 30 of the 36 samples from patients with recurrent/residual disease gave a positive reaction. Thirty-four of the 36 repeat biopsy samples from patients with recurrent/residual disease were positive for Pgp. Correlation analysis, thus showed significant relationship between prognosis and detection of Pgp by immunocytochemistry (r=0.85, p<0.001) and Western blot (r=0.90, p<0.001). Moreover, the odds ratio of a tumor positive for Pgp not responding to chemotherapy was 35.36 (CI 11.03, 113.37). Thus evaluation for Pgp may prove to be a useful prognostic marker for high grade NHL, and may also prove useful in designing or altering chemotherapy protocols in such patients.

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