Here, we propose three new models, each of which uses a different approach to incorporate modelling of non-proportional hazards in the relative survival model developped by Jacques Esteve.

First, we developed a piecewise PH model, then we have introduced a parametric time-by-covariate interaction in the model of Jacques Esteve. Thirdly we have tried to implement spline functions, with Michal Abrahamowicz’s help and to develop a non parametric time-by-covariate interaction.