Study on Giredestrant and Phesgo Combination for Advanced or Metastatic Breast Cancer

Inclusion Criteria

• Have confirmed HER2-positive and estrogen receptor-positive advanced breast cancer that cannot be surgically removed.
• Have at least one tumor that can be measured by scans or other medical tests.
• Have been cancer-free for at least 6 months after completing previous non-hormonal cancer treatments.
• Be in good overall health with an ECOG performance status of 0 or 1, meaning fully active or restricted in physically strenuous activity but ambulatory.
• Have a heart function of at least 50% as measured by specific heart tests.
• Have adequate blood and organ function based on medical tests.
• Women of childbearing potential must agree to use effective contraception during treatment and for 7 months after the last dose of Phesgo.
• Men must agree to use condoms during treatment and for 7 months after the last dose of Phesgo.

Maintenance Phase Inclusion Criteria:

• Complete at least four cycles of initial therapy.
• Have stable disease or better at the last tumor assessment during initial therapy.
• Maintain a heart function of at least 50% during initial therapy.

Exclusion Criteria

• Have received previous non-hormonal anti-cancer therapy for advanced breast cancer, except for one line of hormone therapy.
• Have been treated with certain anti-HER2 drugs, except for specific exceptions.
• Have cancer that progressed within 6 months of finishing anti-HER2 therapy.
• Have unresolved side effects from previous cancer treatments.
• Have a history of significant blood-related side effects from previous treatments.
• Have certain heart conditions or have received high doses of specific chemotherapy drugs.
• Have active or uncontrolled brain cancer spread.
• Have difficulty breathing at rest due to cancer or other conditions.
• Be pregnant or breastfeeding, or planning to become pregnant during the study or within 7 months after the last dose of Phesgo.
• Have received investigational therapy or certain other treatments recently.
• Be participating in another clinical trial.
• Have allergies to study medications.
• Have uncontrolled high blood pressure or significant liver disease.
• Have active heart disease or a history of heart problems.
• Have had major surgery or injury recently.
• Have certain digestive conditions or infections.
• Have a history of other cancers within the last 5 years, except for certain non-threatening types.
• Be unwilling to use hormone therapy if required.
• Be taking certain medications that affect the liver or blood clotting.