Expression of P‐glycoprotein influences resistance against anthracyclines in clinical gastric carcinomas

In 58 human gastric cancers, the expression of P‐glycoprotein (P‐gp) was evaluated immunohistochemically and chemosensitivity was determined using the in vitro succinate dehydrogenase inhibition (SDI) test. Tumors which contained over 75% stained cells were scored as positive, and 14 of 58 cases (24%) were positive. There was no significant correlation between P‐gp expression and clinicopathologic features. The succinate dehydrogenase (SD) activity for each drug of P‐gp positive and negative tumors was as follows: 81.8 ± 15.2% vs. 66.3 ± 16.1% for Adriamycin (ADM), 75.5 ± 14.2% vs. 59.1 ± 17.6% for aclacinomycin A (ACR), 71.7 ± 15.0% vs. 61.1 ± 14.0% for mitomycin C (MMC), and 57.5 ± 18.4% vs. 47.0 ± 16.7% for cisplatin (CDDP). The increase in SD activity was evident in P‐gp positive tumors compared with negative ones in cases of ADM (P = 0.0044), ACR (P = 0.0105), and MMC (P = 0.0353). We suggested that P‐gp expression is closely related to chemosensitivities of human gastric cancers to anthracyclines. © 1994 Wiley‐Liss, Inc.