One of the leading causes of chemotherapy failure in non-Hodgkin's lymphomas (NHLs) is multidrug resistance (MDR). MDR can be associated with expression of members of the family of ABC-transporters. Since a correlation between expression of cyclooxygenase-2 (COX-2) and MDR in various cancer cells was described, the expression of COX-2 and the ABC-transporters MDR1/P-glycoprotein (P-gp), MRP1, MRP2 and BCRP was examined in 56 previously non-treated patients by immunohistochemistry. The data show that: i) P-gp is not expressed in non-treated NHLs; ii) MRP2 can be localized in the nuclear membranes of NHL cells; iii) expression of MRP2 in the cytoplasm membrane correlates with clinical response; iv) elevated expression of BCRP is typical for the patients, who did not respond to primary chemotherapy and for cases with shorter progression-free survival time in a 30 months follow-up; and v) there is a strong correlation between COX-2 and MRP1, MRP2 and BCRP. It can be concluded that: i) BCRP may be a crucial factor involved in primary resistance of NHLs, thus it may be useful for prediction of chemotherapeutic treatment and risk of relapse; and ii) since there is strong correlation between COX-2 expression and MDR in NHLs, the application of COX-2 inhibitors may be considered for chemosensitization.

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