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

Overall survival (OS) is defined as the time from randomization to the date of death due to any cause

Overall response rate (ORR) with confirmed response is defined as the proportion of participants with best overall response (BOR) of confirmed complete response (CR) or confirmed partial response (PR), as per BIRC and according to RECIST 1.1

Clinical benefit rate (CBR) with confirmed response is defined as the proportion of participants with a best overall response of confirmed CR or PR, or SD lasting for a duration of at least 24 weeks. CR, PR and SD are defined as per BIRC review according to RECIST 1.1

Duration of response (DOR) with confirmed response only applies to participants whose best overall response is confirmed complete response (CR) or confirmed partial response (PR) according to RECIST 1.1 based on tumor response data per BIRC review. The start date is the date of first documented response of CR or PR and the end date is defined as the date of the first documented progression or death due to underlying cancer.

Time to response (TTR) is defined as the time from the date of randomization to the first documented response of either complete response (CR) or partial response (PR), which must be subsequently confirmed. CR and PR are based on tumor response data as per BIRC review and according to RECIST 1.1

Progression-free survival (PFS) is defined as the time from the date of randomization to the date of the first documented progression or death due to any cause. PFS will be assessed by the Blinded Independent Review Committee (BIRC) according to RECIST 1.1. Results will be presented by PIK3CA mutation status measured in circulating tumor deoxyribonucleic acid (ctDNA) collected at baseline.

Time to definitive deterioration of Eastern Cooperative Oncology Group (ECOG) performance status (PS) from baseline is defined as the time from the date of randomization to the date when ECOG PS has definitively worsened by at least one category compared to baseline. Deterioration is considered definitive if there is no subsequent improvement in ECOG PS back to the baseline category or better.

Time to definitive (10%) deterioration in global health status/Quality of Life (QoL) and symptom scale scores of the EORTC QLQ-C30 is defined as the time from the date of randomization to the date of the first occurrence of at least a 10% worsening from baseline in the global health status/QoL or symptom scale scores, with no subsequent improvement above this threshold during treatment or until death from any cause. The EORTC QLQ-C30 is a validated questionnaire assessing cancer patients' quality of life over the past week, comprising 30 items across 5 functional scales, 3 symptom scales, 6 single items, and a global health status/QoL scale. Scores range from 0 to 100, with higher scores indicating a higher response level.

Change from baseline in global health status/Quality of Life (QoL) and symptom scale scores of the EORTC QLQ-C30 refers to the variation in scores from baseline across domain scores, health states, overall health status, and index values at each assessment timepoint. The EORTC QLQ-C30 is a validated questionnaire designed to assess the quality of life of cancer patients over the past week. It includes 30 items comprising 5 functional scales, 3 symptom scales, 6 single items, and a global health status/QoL scale. Each scale and item is scored from 0 to 100, with higher scores indicating a higher response level.

Time from randomization to objective tumor progression on next-line treatment or death from any cause (PFS2) is defined as the time from the date of randomization to the earliest occurrence of either documented disease progression on next-line therapy, as assessed by the investigator, or death from any cause.