Study of the Molecular Features of Postmenopausal Women With HR+ HER2-negative aBC on First-line Treatment With Ribociclib and Letrozole and, in Patients With a PIK3CA Mutation, on Second-line Treatment With Alpelisib Plus Fulvestrant

CORE PHASE Inclusion Criteria:

* Patient has an advanced (locoregionally recurrent or metastatic) breast cancer in first line treatment (treatment naïve for the advanced setting).
* Patient is in post-menopause, defined by one of the following:
* Prior bilateral oophorectomy
* Age ≥60
* Age \<60 and amenorrhea for 12 or more months (in the absence of chemotherapy, tamoxifen, toremifen, or ovarian suppression) and FSH and estradiol in the postmenopausal range per local normal range
* Patient has a histologically and/or cytologically confirmed diagnosis of estrogenreceptor positive and/or progesterone receptor positive breast cancer by local laboratory.
* Patient has an 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 (FISH, CISH, or SISH) test is required by local laboratory testing.
* Patient is willing to undergo blood and tumor sample collection for the biological assessments/objectives as scheduled in the protocol.

CORE PHASE Exclusion Criteria:

* Patient who received prior treatment with any CDK4/6 inhibitor.
* Patient who received any prior systemic hormonal therapy or chemotherapy for advanced breast cancer.

Note:

Patients who received neo/adjuvant therapy for breast cancer are eligible. If the prior neo/adjuvant therapy included letrozole or anastrozole, the disease-free interval must be greater than 12 months from the completion of treatment until study entry.

• Patients who received ≤ 28 days of letrozole or anastrozole for advanced disease prior to inclusion in this trial are eligible.

\- Patient is currently using other anti-cancer therapy. Other protocol-defined inclusion/exclusion criteria may apply.

EXTENSION PHASE Inclusion criteria:

* Patient has been discontinued (any reason allowed) from treatment with ribociclib + letrozole in the core phase and is deemed suitable for treatment with alpelisib + fulvestrant in second line. Ribociclib + letrozole must be the last treatment regimen before alpelisib + fulvestrant.
* Patient has PIK3CA mutation as determined in tumor tissue and/or plasma by a Novartis designated laboratory. Results of tissue samples obtained during the core phase (screening or EOT) are acceptable

EXTENSION PHASE Exclusion criteria:

* Patient has received prior treatment with any PI3K inhibitors.
* Patient is concurrently using other anti-cancer therapy. Ribociclib and letrozole used in the core phase must be discontinued at least 7 days prior to day one of the extension study treatment.

All drugs with overlapping toxicities must be discontinued within 7 days and AE resolved to NCI CTCAE v4.03 Grade ≤1 prior to study treatment. Exception to this criterion: patients with any grade of alopecia are allowed to enter the study.