This study is known as a "drug interaction study" and is being done to see how abemaciclib may affect the blood levels of a drug mixture of commonly used drugs (caffeine, warfarin, dextromethorphan, and midazolam) when taken in combination with abemaciclib. Each participant will complete screening and four study periods, with the option to continue to receive abemaciclib in a safety extension phase. All participants will complete a safety follow-up.