Study Assessing the Efficacy and Safety of Alpelisib Plus Fulvestrant or Letrozole, Based on Prior Endocrine Therapy, in Patients With PIK3CA Mutant, HR+, HER2- Advanced Breast Cancer Who Have Progressed on or After Prior Treatments

The study comprised two phases:

• Core Phase: included a treatment phase for all subjects from first subject first treatment (FSFT) until disease progression, unacceptable toxicity, or death until 18 months post last subject first treatment (LSFT) + 1 month safety follow-up (total 19 months post LSFT), discontinuation from the study treatment for any other reason, or sponsor terminates the study. At the start of the Core Phase, subjects were assigned to Cohort A, Cohort B, or Cohort C based on previous therapy as follows:

• Cohort A: alpelisib (300 mg oral QD) + fulvestrant (500 mg intramuscular (IM)) to subjects whose last prior treatment was a CDK4/6i plus any AI;
• Cohort B: alpelisib (300 mg oral QD) + letrozole (2.5 mg oral QD) to subjects whose last prior treatment was a CDK4/6i plus fulvestrant;
• Cohort C: alpelisib (300 mg oral QD)+ fulvestrant (500 mg IM) to subjects who failed prior AI based therapy and whose last prior treatment was systemic chemotherapy or endocrine therapy (as monotherapy or in combination with targeted treatment except CDK 4/6i + AI). Endocrine therapy included letrozole, fulvestrant and CDK 4/6 inhibitor plus fulvestrant.
• Extension Phase: included a treatment phase starting at the end of the treatment Core Phase until last subject last visit(LSLV) (up to 36 months). Following the end of the Core Phase, subjects continuing to derive benefit from study treatment who were not eligible for Post-Study Drug Supply (PSDS) in their country based on local regulations were re-consented and transitioned to the Extension Phase. Subjects continued on their existing study treatment assigned in the Core Phase until disease progression/lack of clinical benefit or any other reason for which the subject may have been discontinued from study treatment. If PSDS became available for a subject, the subject was to be discontinued from the study and to access treatment via PSDS. When subjects discontinued treatment for any reason, the end of treatment visit was performed after discontinuation of the medication , followed by safety follow-up 30 days after last dose.

A total of 340 subjects were planned to be enrolled, with approximately 112 subjects in each cohort. In the Core Phase, 379 subjects were analyzed, with 127 subjects in Cohort A, 126 subjects in Cohort B, and 126 subjects in Cohort C. In the Extension Phase, 11 subjects were analyzed, with 1 subject in Cohort A and 10 subjects in Cohort C.

Key Inclusion Criteria: Subjects eligible for inclusion in the Core Phase of the study fulfilled the following key inclusion criteria:

• Subject was an adult male or female ≥ 18 years of age.
• Subjects with histologically and/or cytologically confirmed diagnosis of estrogen receptor (ER)-positive and/or progesterone receptor (PgR)-positive breast cancer by local laboratory.
• Subjects with a confirmed human epidermal growth factor receptor-2 (HER2)-negative aBC.
• Subjects with gene encoding the p110alpha catalytic subunit of PI3K (phosphatidylinositol-3-kinase) (PIK3CA) mutation.
• In case of women, both premenopausal and postmenopausal subjects were allowed to be included in this study.
• Subjects with documented evidence of tumor progression on or after:

i. Cyclin-Dependent Kinase 4 and 6 inhibitor (CDK4/6i) treatment as last treatment regimen in Cohorts A and B.

ii. aromatase inhibitor (AI) treatment (either in adjuvant or metastatic setting) and received systemic chemotherapy or ET (monotherapy or combination except CDK4/6i + AI) as last treatment regimen in Cohort C. Upon completion of enrollment of Cohort B, subjects who received CDK4/6i + fulvestrant as immediate prior therapy were eligible for Cohort C.

iii. No more than 2 prior anticancer therapies for aBC. iv. Received no more than 1 prior regimen of chemotherapy for the treatment of advanced/metastatic disease was permitted.

v. Recovered to grade 1 or better from any adverse events (AEs) related to previous anticancer therapy prior to study entry (except alopecia or other toxicities not considered a safety risk for the subject at the investigator's discretion).

• Subjects with:

i. Measurable disease, i.e., at least 1 measurable lesion as per RECIST v1.1 criteria; or ii. If no measurable disease was present, at least 1 predominantly lytic bone lesion had to be present.

• Subjects with adequate bone marrow and coagulation function, liver function and renal function as shown by laboratory values.
• Subjects with Eastern Cooperative Oncology Group (ECOG) performance status score of ≤ 2.

Key exclusion criteria were:

• Subjects with a known hypersensitivity to alpelisib, fulvestrant, letrozole, goserelin, or leuprolide or to any of their excipients.
• Subjects with prior treatment with any PI3K inhibitor (PI3Ki).
• Subjects with central nervous system (CNS) involvement unless they met all of the following criteria:

i. At least 4 weeks from prior therapy completion (including radiation and/or surgery) to starting the study treatment, ii. Clinically stable CNS tumor at the time of screening untreated or without evidence of progressions for at least 4 weeks after treatment as determined by clinical examination and brain imaging (magnetic resonance imaging (MRI) or computed tomography (CT) during screening period and stable low dose of steroids for 2 weeks prior to initiating study treatment.

• Subjects with an established diagnosis of diabetes mellitus type I or uncontrolled type II.
• Any concurrent severe and/or uncontrolled medical conditions that would, in the investigator's judgment, contraindicate subject participation in the study (e.g., chronic active hepatitis, severe hepatic impairment, etc.).
• Subjects with a history of noncompliance to medical regimens.
• Subjects with impairment of gastrointestinal (GI) function or GI disease that could significantly alter the absorption of the study drugs based on investigator discretion.
• Subjects with documented pneumonitis/interstitial lung disease which was active and requiring treatment.
• Subjects concurrently using other anticancer therapy. All anticancer therapy had to be discontinued prior to Day 1 of study treatment.
• Subjects who had major surgery within 14 days prior to starting treatment with alpelisib, or did not recover from major side effects.
• Subjects with significant cardiac abnormalities.
• History of acute pancreatitis within 1 year of screening or past medical history of chronic pancreatitis.
• Subjects who did not use highly effective contraception while on alpelisib and through the duration after the final dose of alpelisib (not applicable to postmenopausal women).
• Subjects with unresolved osteonecrosis of the jaw.

Other inclusion/exclusion criteria may apply