Background: Gemcitabine and split-dose cisplatin (GC) is standard first-line therapy for patients with advanced urothelial cancer (UC). Everolimus is an inhibitor of the PI3K/AKT/mTOR pathway, dysregulated in ~35% of UCs. The drug has been shown to have single-agent activity in phase II trials of advanced UC. The safety of combining everolimus with GC in the first-line setting for UC is unknown. Methods: Previously untreated cisplatin-eligible patients with advanced UC were enrolled. Patients received gemcitabine 800 mg/m2 and cisplatin 35mg/m2 on days 1 and 8 with everolimus at dose levels (DL1: 5 mg QOD, DL2: 5 mg daily or DL3: 10 mg daily) for six 21-day cycles. Patients with at least SD continued maintenance everolimus until progression. Restaging evaluations were performed every 2 cycles. The primary objective was to establish the dose-limiting toxicity (DLT) and maximum tolerated dose (MTD) of the three-drug combination. Results: 12 patients were enrolled, 7 with bladder and 5 with upper tract primaries. 4/12 patients completed at least 6 cycles. 0/3 patients at DL1 had DLTs. 3/3 patients at DL2 had DLTs (pancytopenia, hypersensitivity reaction to everolimus and anemia). Following de-escalation to DL1, 2/6 patients in a new DL1 cohort had DLTs (neutropenia and diarrhea, 1/6 patients inevaluable). Grade 3/4 events included anemia (67%), neutropenia (42%), lymphopenia (42%), thrombocytopenia (25%), urinary tract infection (25%), hypomagnesemia (17%), and hypophosphatemia (17%). Tumor responses included: 4 PR (33%), 5 SD (42%), 1 PD (8%), and 2 inevaluable (17%). 2 patients with PR underwent consolidative surgery but eventually progressed. Responses by MSKCC Risk Scores of 0, 1, and 2 were seen in 3/5 (60%), 1/6 (17%), and 0/1 patients, respectively. Median PFS was 3.9 months (95% CI, 3.7-no reached) and median OS was 10.8 months (95% CI, 6.9-not reached). Conclusions: MTD was reached at DL1 for combination gemcitabine, split-dose cisplatin and everolimus, with 2/8 evaluable patients exhibiting DLTs at this dose level. Clinical trial information: NCT01182168