I work in the pharma industry and despite not dealing directly with trials, I need to analyze them sometimes. Usually, you start testin these new medicines as part of a combination with stablished approved drugs OR in patients that didnt respond well to conventional drugs. And most likely, these new medicines usually are approved as part of a combination or in types of cancer / advanced cancers where "there is not much hope". With time and with the increasing knowledge, these drugs can later be approved as monotherapy.