Amcenestrant (SAR439859) Plus Palbociclib as First Line Therapy for Patients With ER (+) HER2(-) Advanced Breast Cancer

Overall Survival (OS)

OS was defined as the interval (in months) from the date of randomization to the date of documented death (due to any cause). In the absence of observation of death, survival time was censored to last date the participant was known to be alive or at the cut-off date, whichever comes first. Analysis was performed by Kaplan-Meier method.

Time frame: From randomization to the death due to any cause or data cut-off date, whichever comes first (maximum duration: 81 weeks)

12-month Progression-free Survival (PFS) Rate

Percentage of participants who were disease progression-free at Month 12 after randomization were reported in this outcome measure. PFS was defined as the time interval (in months) from the date of randomization to the date of first documented tumor progression as per RECIST 1.1 assessed by local radiologist or investigator, or death (due to any cause), whichever comes first. PD as per RECIST 1.1: at least a 20% increase in sum of diameters of target lesions, unequivocal progression of existing non-target lesions. The PFS rate at Month 12 was estimated using the Kaplan-Meier method and provided an estimation of the percentage of participants who were disease progression-free at Month 12 after randomization.

Time frame: Month 12

Percentage of Participants With Objective Response

Objective response was defined as percentage of participants having a partial response (PR) or complete response (CR) according to the RECIST version 1.1 assessed by investigator. As per RECIST 1.1, CR was defined as disappearance of all target and non-target lesions and normalization of tumor marker level. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to less than (\<) 10 millimeters (mm). PR was defined as at least a 30%decrease in the sum of diameters of target lesions, taking as reference the Baseline sum diameters.

Time frame: From randomization to the date of first documented tumor progression, death due to any cause or data cut-off date whichever comes first (maximum duration: 81 weeks)

Duration of Response (DOR)

DOR was defined as time (in months) from first documented evidence of CR or PR until disease progression determined by investigator as per RECIST 1.1, or start of any anti-cancer therapy, or death from any cause, whichever occurs first. For participants with ongoing response at the time of the analysis, DOR was censored at the date of the last valid disease assessment not showing documented progression performed before the initiation of a new anticancer treatment (if any). As per RECIST 1.1, CR was defined as disappearance of all target and non-target lesions and normalization of tumor marker level. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to \<10 mm. PR: at least a 30% decrease in the sum of diameters of target lesions, taking as reference the Baseline sum diameters. PD: at least 20% increase in sum of diameters of target lesions, unequivocal progression of existing non-target lesions. Analysis was performed by Kaplan-Meier method.

Time frame: From the date of first response of CR or PR until disease progression or death, or start of any anti-cancer therapy or data cut-off date, whichever comes first (maximum duration: 81 weeks)

Percentage of Participants With Clinical Benefit

Clinical Benefit was defined as the percentage of participants having a confirmed CR, PR, or stable disease (SD) for at least 24 weeks determined by investigator as per RECIST 1.1, from date of randomization until disease progression, or death, or data cut-off date, or initiation of post treatment anti-cancer therapy, whichever occurs first. As per RECIST 1.1; CR was defined as disappearance of all target, non-target lesions \& normalization of tumor marker level. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to \<10 mm. PR: at least a 30% decrease in sum of diameters of target lesions, taking as reference Baseline sum diameters. SD: neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference smallest sum diameters. PD: at least 20% increase in sum of diameters of target lesions, unequivocal progression of existing non-target lesions.

Time frame: From randomization until disease progression, or death, or data cut-off date, whichever comes first (maximum duration: 81 weeks)

Progression-free Survival on Next Line of Therapy (PFS2)

PFS2 was defined as the time interval (in months) from the date of randomization to the date of first documentation of PD on the next systemic anti-cancer therapy according to investigator, or death due to any cause in the absence of documented PD on the next systemic anti-cancer therapy, whichever occurs first. PD was defined as at least 20% increase in sum of diameters of target lesions, unequivocal progression of existing non-target lesions. Analysis was performed by Kaplan-Meier method.

Time frame: From randomization to date first documented disease progression on the next systemic anti-cancer therapy, or death due to any cause, or data cut-off date, whichever comes first (maximum duration: 81 weeks)

Pharmacokinetics: Plasma Concentrations of Amcenestrant

Amcenestrant plasma concentrations at specified time points were reported. Data for this outcome measure was not planned to be collected and analyzed for Letrozole+Palbociclib arm as pre-specified in protocol.

Time frame: Cycle 1 Day 1: 3 hours (hr) post-dose, Cycle 1 Day 15: pre-dose, Cycle 2 Day 1: pre-dose, 3 hr post-dose, Cycle 2 Day 15: pre-dose, Cycle 3 Day 1: pre-dose, Cycle 4 Day 1: pre-dose, Cycle 7 Day 1: pre-dose, Cycle 10 Day 1: pre-dose

Pharmacokinetics: Plasma Concentrations of Palbociclib

Palbociclib plasma concentrations at specified time points were reported.

Time frame: Cycle 1 Day 1: 3 hr post-dose, Cycle 1 Day 15: pre-dose, Cycle 2 Day 1: pre-dose, 3 hr post-dose, Cycle 2 Day 15: pre-dose, Cycle 3 Day 1: pre-dose, Cycle 4 Day 1: pre-dose, Cycle 7 Day 1: pre-dose, Cycle 10 Day 1: pre-dose

Change From Baseline in European Organization for Research and Treatment of Cancer Core Quality of Life Questionnaire (EORTC-QLQ-C30) Domain Scores

EORTC-QLQ-C30: cancer-specific instrument with 30 questions for evaluation of new chemotherapy \& assessment of participant reported outcome. These include 5 functional scales, 9 symptom scales, \& Global Health Status/quality of life scale (GHS/QoL). All 14 items/domains were scored on scale of 1 (not at all) to 4 (very much) \& GHS/QoL, scored on scale of 1 (very poor) to 7 (excellent). All scales are transformed from raw scores to linear scales ranging 0 to 100. Higher score for functional \& GHS/QoL=higher level of functioning, \& higher score for symptoms scales=higher symptom burden. Least Square (LS) mean and Standard Error (SE) were derived from MMRM model with change from Baseline values as response variable, treatment, time, treatment-by-time interaction, Baseline value and stratifications factors as fixed effect. Average of LS mean change from Baseline values of overall treatment (i.e., each cycle \[Cycle 1 up to Cycle 21\]) for each domain was reported in this outcome measure.

Time frame: Baseline, overall treatment duration (Cycle 1 up to Cycle 21 [i.e., 81 weeks])

Change From Baseline in European Organization for Research and Treatment of Cancer Quality of Life Breast Cancer Specific Module (EORTC-QLQ-BR23) Domain Scores

QLQ-BR23: disease-specific Health-related QOL assesses breast cancer impact \& side effects of treatment. EORTCQLQ- BR23 contains 23 items: multi-item scales \& single-item measures. 4 functional scales (body image, sexual functioning, sexual enjoyment, future perspective) \& 4 scales related to symptoms of disease or treatment (arm symptoms, breast symptoms, systemic therapy side effects, \& upset by hair loss). All items scored 1 (not at all) to 4 (very much). Scores of all scales transformed from raw scores to linear scales ranging 0-100. Higher score for functional scales=better outcome; higher score for symptoms scales=higher symptom burden. LS mean \& SE were derived from MMRM model with change from Baseline values as response variable, treatment, time, treatment-by-time interaction, Baseline value \& stratifications factors as fixed effect. Average of LS mean change from Baseline values of overall treatment (i.e., each cycle \[Cycle 1 up to Cycle 21\]) for each domain was reported.

Time frame: Baseline, overall treatment duration (Cycle 1 up to Cycle 21 [i.e., 81 weeks])

Change From Baseline in European Organization for Research and Treatment of Cancer Quality of Life Breast Cancer Specific Module (EORTC QLQ-BR45) Domain Scores

EORTC QLQ-BR45: comprised of all 23 items from the QLQ-BR23 plus an additional 22 items assessing endocrine therapy symptoms (10 items), endocrine sexual symptoms (4 items), breast satisfaction (2 items), and skin mucosis symptoms (6 items). All items scored 1 (not at all) to 4 (very much). Scores of all scales transformed from raw scores to linear scales ranging 0 to 100. Higher score for functional scales = better outcome; higher score for symptoms scales = higher symptom burden. LS mean and SE are derived from Mixed Model Repeated Measures (MMRM) model with change from Baseline values as response variable, treatment, time, treatment-by-time interaction, Baseline value and stratifications factors as fixed effect. Average of LS mean change from Baseline values of overall treatment (i.e., each cycle \[Cycle 1 up to Cycle 21\]) for each domain (endocrine therapy symptoms, endocrine sexual symptoms, breast satisfaction and skin mucosis symptoms) was reported.

Time frame: Baseline, overall treatment duration (Cycle 1 up to Cycle 21 [i.e., 81 weeks])

Change From Baseline in European Quality of Life Working Group Health Status Measure 5 Dimensions (5D), 5 Levels (5L) (EQ-5D-5L) Score: Visual Analog Scale (VAS) Score

EQ-5D-5L is a standardized measure of health status, provides a simple, generic measure of health for clinical and economic appraisal, and consists of 2 sections: the EQ-5D-5L health state utility index (descriptive system) and the EQ-5D-5L VAS. The Visual Analogue Scale is designed to rate the participant's current health state on a scale from 0 to 100, where 0 represents the worst imaginable health state and 100 represents the best imaginable health state. LS mean and SE are derived from MMRM model with change from Baseline values as response variable, treatment, time, treatment-by-time interaction, Baseline value and stratifications factors as fixed effect. Average of LS mean change from Baseline values of overall treatment (i.e., each cycle \[Cycle 1 up to Cycle 21\]) for VAS was reported in this outcome measure.

Time frame: Baseline, overall treatment duration (Cycle 1 up to Cycle 21 [i.e., 81 weeks])

Change From Baseline in European Quality of Life Working Group Health Status Measure 5 Dimensions (5D), 5 Levels (5L) (EQ-5D-5L) Score: Health Utility Index Value Score

EQ-5D-5L: consists of 2 sections: EQ-5D-5L health state utility index (descriptive system) \& VAS. The EQ-5D descriptive system consists of 5 dimensions: mobility, self-care, usual activities, pain/discomfort \& anxiety/depression. Each dimension has 5 levels: no problems, slight problems, moderate problems, severe problems, \& extreme problems. Response options are measured with 5-point Likert scale (for 5L version). The EQ-5D-5L responses are converted into single index utility score between 0 to 1, where higher score indicates better health state \& lower score indicate worse health state. LS mean and SE were derived from MMRM model with change from Baseline values as response variable, treatment, time, treatment-by-time interaction, Baseline value and stratifications factors as fixed effect. Average of LS mean change from Baseline values overall treatment (i.e., each cycle \[Cycle 1 up to Cycle 21\]) for health utility index value score was reported in this outcome measure.

Time frame: Baseline, overall treatment duration (Cycle 1 up to Cycle 21 [i.e., 81 weeks])

Time to First Chemotherapy

Time to chemotherapy was defined as the time interval (in months) from the date of randomization to the start date of the first chemotherapy after disease progression.

Time frame: From randomization to the start date of the first chemotherapy (maximum duration: 81 weeks)

Number of Participants With Hematological Abnormalities During the Treatment Period

Hematological parameters assessed were anemia, lymphocyte count decreased, neutrophil count decreased, white blood cell decreased, platelet count decreased. Parameters were assessed as per the National Cancer Institute Common Terminology Criteria for Adverse Experience version 5.0 (NCI-CTCAE v 5.0), where Grade 1 = Mild; Grade 2 = Moderate; Grade 3 = Severe; Grade 4 = Potentially Life Threatening. Grade refers to the severity of the AEs. Treatment period was defined as the time from the first dose of study treatments up to 30 days after last dose of study treatment.

Time frame: From first dose of study treatment up to 30 days after last dose of study treatment (maximum duration: 112 weeks)

Number of Participants With Liver Function Abnormalities of Grade 3 and 4 During the Treatment Period

Liver Function parameters assessed were aspartate aminotransferase increased, alanine aminotransferase increased, alkaline phosphatase increased, total bilirubin increased, gamma-glutamyl transferase increased. Parameters were assessed as per the NCI-CTCAE v 5.0, where Grade 1 = Mild; Grade 2 = Moderate; Grade 3 = Severe; Grade 4 = Potentially Life Threatening. Grade refers to the severity of the AEs. Treatment period was defined as the time from the first dose of study treatments up to 30 days after last dose of study treatment. Participants with Grade 3 and 4 liver function abnormalities were reported in this outcome measure.

Time frame: From first dose of study treatment up to 30 days after last dose of study treatment (maximum duration: 112 weeks)