Frequent expression of P‐glycoprotein/MDR1 by nasal T‐cell lymphoma cells

Background. Lethal midline granuloma is now considered to be a malignant lymphoma derived from peripheral T cells or from natural killer cells. The therapeutic outcome of nasal T‐cell lymphoma (NL) treated by conventional chemotherapy for non‐Hodgkin's lymphoma is poor, although some patients have a good response to radiotherapy. To clarify the mechanisms of drug resistance, the expression of P‐glycoprotein (P‐gp)/MDR1, which is the product of the multidrug resistance (MDR) 1 gene, and MDR3 mRNA in NL cells, were examined. Methods. Ten Japanese patients with NL were studied. Nine of these patients were examined before therapy. P‐glycoprotein expression and phenotypes of lymphoma cells were examined by immunohistochemical staining using UIC2 as an anti–P‐gp monoclonal antibody. In one case, the Rhodamine‐123 efflux test was performed. MDR1 and MDR3 mRNA were detected by reverse transcription polymerase chain reaction. Results. Nine of the 10 patients were P‐gp positive. In one of nine, functional P‐gp expression was observed. MDR1 mRNA was detected in all seven examined patients with P‐gp positive NLs, whereas MDR3 mRNA was negative. Retrospectively, patients who received chemotherapy alone had poorer outcome than those treated by combination chemotherapy after irradiation. Conclusion. The poor prognosis for patients with NL treated with chemotherapy may be explained by P‐gp expression of the NL cells. Cancer 1995; 76:2351–6.