Study: NCT05296798

Intervention type: DRUG
Group type: ACTIVE_COMPARATOR
Intervention: Phesgo
Description: Phesgo will be administered subcutaneously (SC) at a fixed non-weight-based dose. In the induction therapy phase, a loading dose (1200 milligram (mg) pertuzumab, 600 mg trastuzumab, and 30,000 units of recombinant human PH20 hyaluronidase \[rHuPH20\]) will be administered in the first cycle (1 cycle is 21 days). In subsequent cycles, maintenance doses (600 mg pertuzumab, 600 mg trastuzumab, and 20,000 units rHuPH20) will be administered once every 3 weeks (Q3W).

Intervention type: DRUG
Group type: EXPERIMENTAL
Intervention: Phesgo
Description: Phesgo will be administered subcutaneously (SC) at a fixed non-weight-based dose. In the induction therapy phase, a loading dose (1200 milligram (mg) pertuzumab, 600 mg trastuzumab, and 30,000 units of recombinant human PH20 hyaluronidase \[rHuPH20\]) will be administered in the first cycle (1 cycle is 21 days). In subsequent cycles, maintenance doses (600 mg pertuzumab, 600 mg trastuzumab, and 20,000 units rHuPH20) will be administered once every 3 weeks (Q3W).

Intervention type: DRUG
Group type: OTHER
Intervention: Phesgo
Description: Phesgo will be administered subcutaneously (SC) at a fixed non-weight-based dose. In the induction therapy phase, a loading dose (1200 milligram (mg) pertuzumab, 600 mg trastuzumab, and 30,000 units of recombinant human PH20 hyaluronidase \[rHuPH20\]) will be administered in the first cycle (1 cycle is 21 days). In subsequent cycles, maintenance doses (600 mg pertuzumab, 600 mg trastuzumab, and 20,000 units rHuPH20) will be administered once every 3 weeks (Q3W).

Intervention type: DRUG
Group type: EXPERIMENTAL
Intervention: Giredestrant
Description: A 30 milligram (mg) capsule of giredestrant will be taken orally once a day on Days 1 to 21 of each 21-day cycle.

Intervention type: DRUG
Group type: OTHER
Intervention: Docetaxel
Description: During the induction therapy phase, the investigator's choice of taxane-based chemotherapy (i.e., docetaxel or paclitaxel) will be administered after Phesgo. Docetaxel will be administered at 75 milligrams per metre squared of body surface area (mg/m2) intravenously over 60 (±10) minutes on Day 1 of each cycle for 4 to 8 cycles (a cycle is 21 days); this dose may be escalated to 100 mg/m2 if the initial dose was well tolerated.

Intervention type: DRUG
Group type: OTHER
Intervention: Paclitaxel
Description: During the induction therapy phase, the investigator's choice of taxane-based chemotherapy (i.e., docetaxel or paclitaxel) will be administered after Phesgo. Paclitaxel will be administered at 80 milligrams per metre squared of body surface area (mg/m2) intravenously over a minimum of 1 hour on Days 1, 8, and 15 of each cycle for 4 to 8 cycles (a cycle is 21 days); this weekly regimen is considered as one complete cycle whenever 3 weekly doses are given.

Intervention type: DRUG
Group type: ACTIVE_COMPARATOR
Intervention: LHRH Agonist
Description: A luteinizing hormone-releasing hormone (LHRH) agonist will be administered every 28 days to pre- and peri-menopausal women and all male participants while receiving giredestrant in Arm B. An LHRH agonist may be administered to male participants and pre- and peri-menopausal female participants receiving tamoxifen in Arm A, and should be administered to those receiving an aromatase inhibitor in Arm A. The investigator will determine and supply the appropriate LHRH agonist locally approved for use in breast cancer. The LHRH agonist will be administered according to local prescribing information.

Intervention type: DRUG
Group type: EXPERIMENTAL
Intervention: LHRH Agonist
Description: A luteinizing hormone-releasing hormone (LHRH) agonist will be administered every 28 days to pre- and peri-menopausal women and all male participants while receiving giredestrant in Arm B. An LHRH agonist may be administered to male participants and pre- and peri-menopausal female participants receiving tamoxifen in Arm A, and should be administered to those receiving an aromatase inhibitor in Arm A. The investigator will determine and supply the appropriate LHRH agonist locally approved for use in breast cancer. The LHRH agonist will be administered according to local prescribing information.

Intervention type: DRUG
Group type: ACTIVE_COMPARATOR
Intervention: Optional Endocrine Therapy of Investigator's Choice
Description: For participants in Arm A, optional endocrine therapy of investigator's choice is allowed based on the standard of care, and it can include an aromatase inhibitor or tamoxifen with or without an LHRH agonist, or gonadal ablation. The decision to include or exclude this option must be made prior to randomization.