Abstract Chemotherapy resistance is a major hurdle in high-grade serous epithelial ovarian cancer (HGSC) management. We previously reported differential expression of interferon inducible genes in pre-treatment tumours from chemoresistant and sensitive HGSC tumors. STAT1 expression was evaluated as a prognostic and predictive biomarker via immunohistochemistry in Phase I (n = 183) and Phase II (n = 550) biomarker validation studies conducted on HGSC tumours accrued from the Terry Fox Research Institute- Canadian Ovarian Experimental Unified Resource (TFRI-COEUR). Tumor STAT1 expression levels significantly correlated with the density of tumor infiltrating CD8+ T lymphocytes in both Phase I and Phase II cohorts. STAT1 expression significantly associated with progression free survival and response to chemotherapy in both Phase I and Phase II validation studies. Significant positive correlation between STAT1 expression levels and intratumoral CD8+ T cell density was observed. Intratumoral CD8+ T cell infiltration did not associate with progression free survival or response to chemotherapy in both cohorts. Interestingly, the prognostic relevance of CD8+ T cell was enhanced in combination with STAT1 in both cohorts. These findings provide evidence that STAT1 as an independent biomarker and a combination of CD8+ T cell infiltration with STAT1 could be novel immune-based prognostic and predictive biomarkers in HGSC. Findings from the current study will aid in patient stratification for novel immunomodulatory therapies for the management of chemotherapy resistance in HGSC. Citation Format: Katrina K. Au, Liliane Meunier, Cécile Le Page, Charles H. Graham, Andrew WB Craig, Timothy Childs, Julie-Ann Francis, Jeremy Squire, Anne-Marie Mes-Masson, Madhuri Koti. Association of interferon inducible genes with tumor immune microenvironment and chemotherapy resistance in high-grade serous epithelial ovarian cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 441.