The BELLE-2 was a randomized phase III, double-blind, placebo-controlled, study, in which breast cancer patients ER+/HER2- with advanced or metastatic disease and under disease progression after chemo-endocrine therapies were randomized to receive Buparlisib plus fulvestrant versus placebo plus fulvestrant [308]. The gene discussed is ESR1; the disease is metastatic neoplasm.