Purpose: There is evidence that IFNg plays an important role in ovarian cancer development. IFNg produces numerous antitumor effects and it may be evasion of these effects which allows tumor progression. We postulate that genetic instability in tumor cells may lead to modulation of expression of the IFNg receptor, thus leading to altered tumor biology and patient prognosis.This hypothesis would support the theory of immunoediting in ovarian cancer. Experimental Design: Using tissue microarray

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... chnology of 339 primary ovarian cancers, the expression of IFNg receptor was assessed immunohistochemically. Coupled to a comprehensive database of clinicopathologic variables, its effect on these factors was studied. Results: Tumors expressing high levels of IFNg receptor had significantly improved survival (P = 0.017) compared with tumors expressing low levels of the receptor; this was also seen with complete receptor loss (P = 0.014). Factors shown to predict prognosis independently of each other were the following: age, International Federation of Gynecologists and Obstetricians stage, and the absence of macroscopic disease after surgery.The level of IFNg receptor expression and complete receptor loss were independently predictive of prognosis on multivariate analysis.There was no correlation between receptor status and any of the standard clinicopathologic variables. Conclusions: Loss of IFNg receptor independently predicts poor prognosis in ovarian cancer. Loss of receptor expression may be responsible for the limited success in the therapeutic use of IFNg in ovarian cancer trials and highlights a subgroup of high expressing IFNg receptor tumors which are more likely to be susceptible to such treatments.