Relationship of the expression of the multidrug resistance gene product (P-glycoprotein) in human colon carcinoma to local tumor aggressiveness and lymph node metastasis.

P-glycoprotein mediates classic multidrug resistance by functioning as an efflux pump that excretes lipophilic chemotherapeutic drugs from cancer cells. We now report an association of P-glycoprotein in colon carcinomas with another tumor property, i.e., enhancement of local tumor aggressiveness. P-glycoprotein was detected with monoclonal antibody immunohistochemistry in 65 of 95 primary colon adenocarcinomas, which were stage B1 or greater. In all but 1 of the 95 cases, solitary invading carcinoma cells were present at the leading edge of the tumor. This subpopulation of invasive carcinoma cells expressed P-glycoprotein (P-Gp+) in 47 of the 95 surgically resected colon specimens. Cases were grouped on the basis of the presence (Group 1, 47 cases) or absence (Group 2, 48 cases) of P-Gp+ invasive carcinoma cells. There was a significantly greater incidence of vessel invasion (P less than 0.001) and lymph node metastases (P less than 0.01) in Group 1 cases. Groups 1 and 2 did not differ with respect to tumor size, depth of invasion of the bowel wall, histological grade, maximum tumor size, mitotic index, mucin production, or presence of perineural invasion (P greater than 0.1). Our findings indicate that P-Gp+ invasive colon cancer cells may have an increased potential for dissemination, suggesting that P-glycoprotein may influence cell behavior.