In this study, 212 untreated primary pulmonary and pleural neoplasms were studied immunohistochemically with the monoclonal antibody HYB-612 which detects the multidrug resistance (MDR)-related P-glycoprotein (gp180). A tumor was considered positive for the expression of the MDR phenotype, even if a single rare positive cell was detected. Using this criterion, all of the various histologic subtypes were found to express MDR to varying degrees. The frequency of expression of this phenotype was found to be notably higher in non-small-cell carcinomas than in small-cell carcinomas. These findings are consistent with the known clinical responses of these neoplasms. The detection of gp180 in untreated lung neoplasms may be predictive of the responsiveness of neoplasms to chemotherapeutic agents. In addition, its presence or absence might be useful in determining the appropriate treatment protocol for given patients.

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