Background: Despite countless clinical trials being conducted, little has changed over the last decade in the chemotherapies available for glioblastoma (GBM) with survival remaining poor. Meaningful advances in treating this deadly malignancy may rely on precision medicine. We discovered a novel pharmacogenomic biomarker for enzastaurin (enz) in treating lymphoma (lymph). We evaluated if this biomarker can be used to predict enz response in GBM. Methods: Biomarker discovery was performed by a genome-wide screen using DNA extracted from blood samples from a ph 3 enz lymph trial and confirmed in an independent ph 2 enz lymph trial. The biomarker was then evaluated for its predictability in GBM using the archived DNA samples from a prior ph 1/2 enz GBM trial. Results: A novel biomarker, Denovo Genomic Marker 1 (DGM1), a germline polymorphism on chromosome 8, was found to be highly correlated with response to enz in the two lymph trials. Using DNA extracted from blood of pts from the single-arm ph 1/2 study of newly diagnosed GBM receiving enz added to radiation and temozolomide (tmz), we found median OS for DGM1+ pts treated with enz was 18 mon vs 12.8 mon for DGM1- pts, HR (95% CI) 0.68 (0.25, 1.81), p = 0.12. In addition, we found pts in the GBM study receiving a mean daily dose of enz ≥ 245 mg had an OS of 19.8 mon vs 14.9 mon for pts receiving a mean daily dose of < 245 mg [HR (95% CI) 0.55 (0.34, 0.90)]; enz 500 mg/day was used in the lymph studies. Conclusions: These data are supportive of DGM1 as a potentially predictive biomarker for enz response in both lymph and GBM. There is an ongoing biomarker-driven pivotal ph 3 study in lymph at 500 mg/day, and DGM1 in GBM will be further evaluated in a planned randomized ph 2b study in newly diagnosed GBM with 500 mg/day of enz in combination with tmz.