A time-to-event endpoint is the time taken until a pre-defined event takes place, once groups in a trial start to receive treatment or placebo. There are several kinds of time-to-event endpoints. For example, time-to-progression (TTP) is the time between randomisation of people to groups within a trial, and disease progression. Disease progression in this case must be defined, and it must be specific and measurable. For example, the growth of a particular tumour type by a minimum amount may be used as an indicator of disease progression.