The aim of this study was to investigate the expression of P-glycoprotein (Pgp), multidrug resistance-related protein-1 (MRP1), and lung resistance-related protein (LRP) in response to chemotherapy in untreated small cell lung cancer (SCLC). Immunohistochemical analyses were performed on multiple nonconsecutive sections of biopsy specimens to detect Pgp, MRP1, and LRP expression in 40 patients with SCLC before chemotherapeutic induction. Response to chemotherapy was evaluated by clinical and radiological methods. The patients were divided into a good response group (n = 20) and a poor response group (n = 20). No significant differences in prognostic factors (Karnofsky performance status, tumor size, or tumor stage) were found between the two groups of patients. The difference in positive Pgp and MRP1 expressions between the good and poor response groups was significant. However, the difference in LRP expression was not significant. We conclude that chemotherapy response of patients with SCLC was related to either Pgp or MRP1 but not LPR expression.
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