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Background: Testicular germ cell tumor (GCT) is the most common cancer in young men between 15 and 35 years of age. Cisplatin-based combination chemotherapy will cure 70% of patients with metastatic GCT. Patients who relapse can still be cured with salvage standard-dose or high-dose chemotherapy. However, about 15% of patients with relapsed/refractory GCT are incurable. NAD(P)H:quinone oxidoreductase 1 (NQO1) is a two-electron oxidoreductase elevated in several tumor types compared to normal tissue. NQO1 detoxifies quinones and reduces oxidative stress. NQO1 bioactivatable drugs induce DNA damage in cells overexpressing NQO1, but not in cells lacking it, hence delivering tumor-selective damage and cell death. Alterations in catalase expression can cause cytoprotection. The ratio of NQO1:catalase activities is presumed to be a predictive marker for therapeutic activity of NQO1 bioactivatable drugs. There is no existing data on NQO1 or catalase expression in GCTs. Methods: Patients with testicular or extra-gonadal GCT who had surgery between January 2016 and December 2018 were identified from the Indiana University Melvin and Bren Simon Cancer Center Tissue Bank database. Patients with non-seminomatous GCT (NSGCT) of testis or primary mediastinal NSGCT were selected and specimens obtained. Immunohistochemistry staining was performed on tumor tissue to determine the quantity and intensity of NQO1 and catalase expression. Results: NQO1 and catalase expression were determined in 16 patients. Thirteen specimens stained moderately to strongly positive for NQO1. Only 1 specimen stained negative. Conversely, no specimen stained strongly positive for catalase, and only 2 stained moderately positive. Fourteen specimens were catalase deficient or only mildly positive for catalase. The details of the immunostaining is summarized in the table below. Immunohistochemistry staining for NQO1 and catalase in GCTImmunostainNegative(0)Mildly positive (50%)NQO1Quantity01114Intensity0547Combined score1267CatalaseQuantity3472Intensity31120Combined score7720 Conclusions: NSGCTs appear to have high levels of NQO1 and deficiency of catalase. NQO1 bioactivatable agents could serve as a potential therapeutic approach in patients with refractory testicular GCTs. Citation Format: Neda Hashemi Sadraei, Nabil Adra, Constance Temm, Kenneth A. Kesler, Muhammad T. Idrees, David A. Boothman, Lawrence Einhorn. Tissue analysis of NAD(P)H: quinone oxidoreductase (NQO1) and catalase expression in patients with germ cell tumors (GCT) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5169.