This is a first-in-human, open-label, multicenter, Phase 1a/1b dose escalation dose finding, and dose expansion study to evaluate safety, tolerability, pharmacokinetics (PK), and preliminary antitumor activity of ATV-1601 as monotherapy in participants with advanced or metastatic solid tumors with the AKT1 E17K mutation, and in combination with fulvestrant in participants with breast cancer that has the AKT1 E17K mutation. This study has a dose escalation and expansion phase with ATV-1601, and an escalation and expansion phase in combination with Fulvestrant.
