Inclusion Criteria:  Participant is an adult ≥18 years old at the time of consent Participant with ABC (loco regionally recurrent or metastatic) not amenable to curative therapy. Participant with a histologically and/or cytologically confirmed diagnosis of ER-positive and/or PR-positive breast cancer by local laboratory. Participant with a confirmed HER2-negative ABC. Participant with a pathology report confirming PIK3CA mutant status by a certified laboratory using a validated PIK3CA mutation assay (from either tissue or blood). Participant is a man or a pre- or post-menopausal woman. Participant is willing to operate a smartphone compatible with the software of the medical device and willing to manage applications Participant is willing to use the telemedicine platform and to follow the remote participant monitoring procedure. Participant has signed an informed consent form before any trial  Exclusion Criteria:  Participant has received prior treatment with any PI3K, mTOR or AKT inhibitor. Participant with known hypersensitivity to alpelisib or fulvestrant, or to any of the excipients of alpelisib or fulvestrant. Participant participated in a prior investigational study within 30 days prior to the start of trial treatment or within 5 half-lives of the trial treatment, whichever is longer.  Other protocol-defined inclusion/exclusion criteria may apply.