ESR1 and breast cancer: More recently, results from the phase III BELLE-3 trial showed a modest, albeit statistically significant, improvement in PFS in the combined buparlisib- and fulvestrant-treated arm compared to fulvestrant alone in ER+ advanced breast cancer patients after progression on endocrine therapy and everolimus (3.9 vs. 1.8 months, p = 0.0003) [34].