Preferential expression of the multidurg‐resistance‐associated protein (MRP) in adenocarcinoma of the lung

The expression of multidrug-resistance-associated protein (MRP) was assessed in various types of untreated lung cancer using an immunohistochemical technique. MRP was abundantly expressed in 28 of 59 adenocarcinoma specimens (47%) and its expression was associated with the degree of glandular differentiation of the tumor. MRP expression in well-differentiated adenocarcinomas (56%) was higher than in poorly differentiated adenocarcinomas (22%) (p < 0.01). lower--20% in squamous-cell carcinomas, 20% in large-cell carcinomas and 0% in small-cell carcinomas and carcinoids. RT-PCR showed that the MRP-positive adenocarcinomas and squamous-cell carcinomas expressed mrp mRNA significantly. Immunoelectron microscopically, MRP was localized in the plasma membrane and rough endoplasmic reticulum. It is thus important to take MRP into account when considering chemotherapy for lung cancers because levels of mdr I gene product, another multidrug-resistance gene family, are low in untreated lung cancers.