PRS-343 in Combination With Atezolizumab in HER2-Positive Solid Tumors

This is a multicenter, open-label Phase 1b study to determine the MTD and RP2D and to assess the safety and efficacy of PRS-343 administered in combination with atezolizumab, a PD-L1 antibody, in previously treated advanced or metastatic HER-2 positive solid tumors (e.g., bladder, breast and gastrointestinal). The study will include a dose escalation period followed by an expansion period. PRS-343 and atezolizumab will be given intravenously once every three weeks (Q3W). All available safety data, emerging PK, pharmacodynamic data, and dose limiting toxicities (DLTs) will be considered in guiding the Safety Committee's decisions regarding subsequent doses to be tested during the escalation phase of the study. Once the MTD and RP2D have been established, an expansion cohort will be enrolled. One treatment cycle is defined as 21 days (3 weeks).