Background: Autophagy is a catabolic process triggered in cells during periods of stress to enable their survival. Established tumors utilize autophagy to survive periods of metabolic or hypoxic stress. Inhibition of early stage autophagy can rescue cancer cells, while inhibition of late stage autophagy will lead to cell death due to accumulation of damaged organelles. The antimalarial drugs CQ and HCQ inhibit late phase autophagy. The goal of our study is to assess the safety, tolerability and activity of combining CQ/HCQ with CG in advanced solid tumor patients who either progressed on other therapies or in whom CG is a therapeutic option. Methods: This single institution phase 1 dose-escalation study was designed to evaluate the maximum tolerated dose (MTD) of CQ, later substituted with HCQ, in combination with CG in patients with previously treated advanced solid tumors. Secondary objectives were to determine ORR, PFS and OS. A starting dose of 50 mg of CQ/HCQ was used in conjunction with CG, and increased in increments of 50 mg in each dose cohort. Grade 3 or greater toxicity that is treatment-related, and was not self-limited, or controlled in less than 7 days was considered dose limiting toxicity (DLT). Results: Twenty-three patients were enrolled with a median follow up of 6 months. HCQ 100 mg was found to be the MTD in combination with CG with ≥Grade 3 thrombocytopenia and/or neutropenia as dose-limiting. Median OS was 11 months, and the 1- and 3- year overall survival rates were 30% and 7%, respectively. Median progression free survival was 5 months and the 6-, 12-, and 18-months progression-free survivals were 48%, 21% and 14%, respectively (Table). Conclusions: The MTD identified for CQ/HCQ was lower than previously reported with concomitant use of chemotherapeutic regimes, likely due to the myelosuppressive nature of CG. Clinical trial information: NCT02071537