Immunohistochemical analysis of drug resistance-associated proteins in ovarian carcinomas

Loss of function of the tumor suppressor gene p53, increased expression of glutathione-S-transferase pi (GST pi) and the major vault protein are involved in drug resistance of ovarian carcinomas. However, a study comparing these factors has not yet been performed. Therefore, paraffin-embedded material of 213 ovarian tumors with well-documented follow-up was used for immunohistochemical analysis of p53 protein, GST pi, and major vault protein (antibodies LRP-56, LMR-5). Forty-six percent of the cases showed nuclear p53 accumulation. Strong immunoreactivity for GST pi, LRP-56, and LMR-5 was seen in 50%, 36%, and 47%, respectively. p53 positivity was most often found in serous carcinomas (p < 0.05). Strong GST pi expression was the only factor that correlated with clinical resistance to chemotherapy (p = 0.04). In the whole group, as well as in FIGO III cases stratified for residual disease less than or equal to and >2 cm, p53 and GST pi correlated with an adverse outcome (p = 0.01 for p53 and p = 0.04 for GST-pi). Strong LRP-56 or LMR-5 staining was associated with a tendency towards poorer prognosis, without reaching statistical significance. In multivariate analysis for FIGO III, only residual disease and p53 proved to be independent prognostic factors. Our observations confirm the prognostic significance of p53 accumulation in ovarian carcinomas. Only GST pi immunoreactivity was significantly correlated with drug resistance.