General notation
In the following, we will introduce the notation used by us. A summary is provided in Table 1. The term “survival” will be used to refer to time-to-event endpoints in general, including particularly PFS, and the term “time point” to refer to the predefined time of the measurement or assessment of a patient’s survival status. We assume that a patient’s survival is measured at discrete time points A key concept of survival analysis is censoring. Since in early phase II trials the time-to-event outcomes are typically treated as binary endpoints with primary evaluation at a specific time point, for which censoring technically does not exist, censoring due to loss to follow-up is commonly treated as failure in order to follow a conservative analysis strategy. Typically, this is expected to happen infrequently, because these trials are very small and follow-up is rather short. However, if the interim analysis is performed before all recruited patients have had their long-term outcome observed, there is administrative censoring during the interim. Patients who have been censored in this way, are taken into account in equations (Glossary of terms.