Expression of glutathione S-transferase pi and cisplatin resistance in human ovarian cancer

Glutathione S-transferase pi (GST pi) expression in tumor cells is thought to relate to cisplatin resistance. We attempted to clarify immunohistochemically the correlation between GST pi expression and clinical response in ovarian cancer. Fifty-nine patients with ovarian cancer underwent initial debulking surgery and received from three to five courses of cisplatin-based chemotherapy after surgery. Immunostaining for GST pi was performed on formalin fixed sections of the patients' tumor by the streptoavidin-biotin-peroxidase complex method. Positive staining of GST pi was observed diffusely in nuclei and cytoplasm of cancer cells. Of 59 tumors, 38 (64.4%) were GST pi positive. Twenty-three of 25 patients (92.0%) who showed no response to chemotherapy had GST pi positive tumor cells. The predictive value of positive GST pi staining for drug resistance was 79.3% (23/29). The 5-year survival rate of patients with GST pi positive tumors was significantly lower than that of those with GST pi negative tumors by the Kaplan-Meier method (P < 0.01). The results suggest that overexpression of GST pi is related to resistance to cisplatin and to prognosis in patients with ovarian cancer.