This study looks at how safe and effective a drug called LOXO-435 is for treating cancer. It focuses on cancers with a change in a gene named FGFR3. The study lasts up to 30 months (2.5 years) and may go on longer if the cancer doesn't grow. There are two main parts: finding the right dose and seeing how well it works. LOXO-435 will be tested alone or with another drug called pembrolizumab in some cases. The study is for people with advanced solid tumors or metastatic urothelial cancer (a type of bladder cancer) that tests positive for FGFR3 changes. Participants will need to provide cancer tissue samples and meet other health requirements to join.

• The study could last up to 2.5 years or longer.
• Some tests and treatments involve more visits to the clinic.
• Participants must meet specific health criteria to join.