ERBB2 and breast cancer: In the phase III trial of buparlisib plus fulvestrant in hormone receptor-positive/epidermal growth factor receptor-2 negative (HR+/HER2-) advanced breast cancer, the combination of fulvestrant and buparlisib significantly prolonged progression-free survival, but the occurrence of severe side effects was higher than that of the placebo group, at 23% and 16%, respectively.49