Expression of glutathione S-transferase pi (GST-pi) in human malignant ovarian tumors

In recent years, glutathione S-transferase pi (GST-pi) has attracted much attention and has been studied as a mechanism of multidrug resistance of tumors to anticancer drugs. In the present study, we immunohistologically measured the expression of GST-pi in tumor tissues using surgical specimens obtained from patients with malignant ovarian tumors.

Of 137 patients with malignant ovarian tumors treated and managed during a period of 20 years since the establishment of Tsukuba University Hospital, 117 patients were selected as subjects because of the presence of complete data on their clinical courses as well as paraffin blocks preserved in a good condition. GST-pi in these specimens was immunohistochemically stained to determine the correlation between GST-pi stainability and clinical outcomes. Stainability was graded as 0 when GST-pi was completely absent, 1 when less than 20% of tumor cells were stained, 2 when 20--60% were stained, and 3 when more than 60% were stained.

When the correlation between stainability and clinical outcomes was analyzed with Kaplan--Meier method, excluding stage Ia cases that did not receive adjuvant chemotherapy at our hospital, significantly better clinical outcomes were observed in the low stainable group, compared with the high stainable group (P<0.01--0.05, Cox--Mantel test, Wilcoxon's test).

Since the stainability for GST-pi was high in tumors of histological types with strong resistance to anticancer drugs, and better clinical outcomes were observed in cases having a lower stainability score, the expression of GST-pi was thought to play some role in the resistance of malignant ovarian tumors to anticancer drugs.