Sample size determination
In literature, discontinuation of adjuvant hormone therapy is reported in 20% of cases. The option of offering patients a web-application rather than an accompaniment by a standard follow-up would appear relevant if it allows to observe a difference in discontinuation rate of at least 10%. According to a two proportion z-test, with a two-sided alpha risk of 5% and a power of 80%, 398 patients (199 per arm) are required to observe a significant difference in the discontinuation rate of at least 10%, assuming an adherence failure rate of 20% in the control arm. To take into account a 10% drop-out rate, we plan to enroll 438 patients overall (219 per arm).