Study to Assess the Efficacy and Safety of Alpelisib Plus Fulvestrant in Participants With HR-postitive (HR+), HER2-negative, Advanced Breast Cancer After Treatment With a CDK4/6 Inhibitor and an Aromatase Inhibitor.

Inclusion Criteria:

- Participant is an adult ≥ 18 years old at the time of informed consent and has
signed informed consent before any trial related activities and according to local
guidelines.

- If female, then the participant must be in postmenopausal status. Postmenopausal
status is defined either by: prior bilateral oophorectomy, age ≥60 or age <60 and
amenorrheic for 12 or more months in the absence of chemotherapy, tamoxifen,
toremifene, or ovarian suppression and follicle-stimulating hormone (FSH) and
estradiol in the postmenopausal range per local normal range.

- Participant has a histologically and/or cytologically confirmed diagnosis of ER+
and/or PgR+ breast cancer by local laboratory.

- Participant has HER2-negative breast cancer defined as a negative in situ
hybridization test or an IHC status of 0, 1+ or 2+. If IHC is 2+, a negative in situ
hybridization (Fluorescent in situ hybridization (FISH), Chromogenic in situ
hybridization (CISH), or Silver-enhanced in situ hybridization (SISH)) test is
required by local laboratory testing.

- Participant has at least one measurable lesion as per RECIST v1.1 criteria as
assessed by Investigator (a lesion at a previously irradiated site may only be
counted as a target lesion if there is clear sign of progression since the
irradiation).

- Participant has recurrence or progression of disease during or after combined AI
(i.e. letrozole, anastrozole, exemestane) and CDK4/6 inhibitor therapy. The combined
AI and CDK4/6 inhibitor therapy does not need to be the latest treatment regimen
(including adjuvant setting).

- Participant has received ≤2 prior lines of systemic therapies overall in the
metastatic setting, of which a maximum of 1 line of prior treatment with
chemotherapy (except for neoadjuvant/ adjuvant chemotherapy).

- Participant must show the presence of a PIK3CA mutation(s) determined in tumor
tissue prior ro enrollment either by a Novartis designated laboratory or in tumor
tissue or plasma ctDNA by a local laboratory using a Food and Drug Administration
(FDA)-approved PIK3CA Companion Diagnostics (CDx) test for alpelisib or the CE-IVD
QIAGEN Therascreen® PIK3CA RGQ PCR test.

Exclusion Criteria:

- Participant with symptomatic visceral disease that makes the participant ineligible
for endocrine therapy (ET) per the investigator's best judgment.

- Participant who relapsed with documented evidence of progression more than 12 months
from completion of (neo)adjuvant endocrine/endocrine-based therapy with no treatment
for metastatic disease

- Participant has received prior treatment with fulvestrant, any oral selective
estrogen receptor degrader (SERDs), any Phosphatidylinositol-3-Kinase (PI3K),
mammalian Target of Rapamycin (mTOR) or Protein Kinase B (AKT) inhibitor

Other Inclusion and Exclusion Criteria do apply