A Study of Felmetatug Vedotin/SGN-B7H4V in Advanced Solid Tumors

The purpose of the study is to test the safety of the medicine called Felmetatug Vedotin alone and with pembrolizumab in participants with solid tumors. It will also look at the side effects of this medicine. A side effect is anything a medicine does to the body besides treating the disease. This study is seeking for participants who either have cancer: * that has spread in the body near where it started (locally advanced) and cannot be removed (unresectable), * has spread through the body (metastatic), or have some cancer left over after surgery. This study will have five parts. * Parts A and B of the study will find out how much Felmetatug Vedotin should be given to participants. * Part C will use the amount found in Parts A and B to find out how safe Felmetatug Vedotin is and if it works to treat solid tumor cancers. * Part D will find out if and how much Felmetatug Vedotin can be given with pembrolizumab. * Part E will use the amount found in Part D to find out how safe Felmetatug Vedotin with pembrolizumab is and if it works to treat triple negative breast cancer.