This is a 2-part study.
In Part 1 Safety Run-in, eligible participants will be allocated to treatment with sac-TMT + pembrolizumab + bevacizumab.
In Part 2, all participants receive standard of care induction treatment. Eligible participants whose cancer does not progress then begin maintenance treatment and are randomized to receive pembrolizumab or sac-TMT + pembrolizumab. All participants in Part 2 maintenance treatment may also receive bevacizumab at the investigator's discretion.