Results of phase I plus expansion cohorts of cabozantinib (Cabo) plus nivolumab (Nivo) and CaboNivo plus ipilimumab (Ipi) in patients (pts) with with metastatic urothelial carcinoma (mUC) and other genitourinary (GU) malignancies.

515Background: Tolerability and efficacy of CaboNivo and CaboNivoIpi were demonstrated in the initial phase I cohort, prompting longer follow-up and the addition of expansion cohorts to further evaluate both combinations Methods: Phase I cohort had 7 dose levels (DL). Recommended phase 2 doses for CaboNivo=Cabo 40mg/Nivo 3mg/kg (DL2) & CaboNivoIpi=Cabo 40mg/Nivo 3mg/kg/Ipi 1mg/kg (DL6) (Nadal ESMO 2017).In expansion cohorts, pts were treated: [1] DL8: Cabo 40mg/Nivo 1mg/kg/Ipi 3mg/kg; [2]DL2: mUC, metastatic renal cell carcinoma (mRCC), adenocarcinoma bladder (AcB): post-PD-1-PDL1 inhibitor mUC (p-mUC), and [3] DL6 mRCC. Objectives: safety, objective response rate (ORR), duration of response (DOR), progression-free survival (PFS) & overall survival (OS). Results: 75 pts enrolled. Median age 59 yo. 83% male, 17% female. 47 treated with CaboNivo (mUC n=24; AcB n= 9; germ cell tumor (GCT) n= 5; castrate-resistant prostate cancer (CRPC) n= 4; bladder squamous cell carcinoma (SCC) n= 2; penile n=1; mRCC n= 7)....