Expression of multidrug resistance gene (mdr-1) mRNA in gastric and colorectal cancers.

Fresh surgical specimens of 52 gastric cancers and 25 colorectal cancers were analyzed for the expression of multidrug resistance (mdr-1) gene mRNA with non-isotopic in situ hybridization (ISH) using a biotin-labeled oligonucleotide probe. The mdr-1 mRNA was expressed in 15.4% in cancerous portions and 1.9% in non-cancerous portions of gastric cancers (p < 0.02). In colorectal cancers, the mdr-1 mRNA was positive in 36% in cancerous portions and 28% in non-cancerous portions. In gastric cancers, the well-differentiated type showed a significantly higher positive rate than the poorly differentiated type (p < 0.01). These results suggest that the mdr-1 mRNA expression in gastric and colorectal cancers is related to the degree of cellular differentiation.