Study on Trastuzumab Deruxtecan for Patients with HER2-low or HER2 IHC 0 Metastatic Breast Cancer

Inclusion Criteria

• Must sign a consent form to participate.
• Agree to provide a new or previous biopsy sample from the primary or metastatic cancer site.
• Have a confirmed diagnosis of breast cancer that is either:
  • Unresectable (cannot be removed by surgery) or metastatic (has spread to other parts of the body).
  • Hormone receptor-negative or hormone receptor-positive.
  • HER2-low (IHC 1+ or IHC 2+/ISH-) or HER2 IHC 0 status, based on specific guidelines.
  • Never been HER2-positive in past tests.
  • Not previously treated with anti-HER2 therapy for metastatic cancer.
• Have had one or two previous treatments for metastatic cancer.
• For hormone receptor-positive HER2-low metastatic breast cancer:
  • Cancer returned less than 2 years after starting hormone therapy, or
  • Cancer progressed on a CDK4/6 inhibitor regimen within 12 months after completing hormone therapy, or
  • Cancer progressed within the first 12 months of CDK4/6 treatment in the metastatic setting.
• Have at least one measurable tumor by CT or MRI scans.
• Can have small, untreated, and stable brain metastases.
• Have a performance status score of 0 or 1, indicating full activity or some restriction in strenuous activities.
• Have a life expectancy of at least 12 weeks.
• Have a heart function of 50% or higher.
• Have adequate organ and bone marrow function.
• Have completed a sufficient washout period from previous treatments.
• Agree to use effective contraception if of childbearing potential.

Exclusion Criteria

• Have had previous treatment with an antibody drug conjugate (ADC).
• Have uncontrolled or significant heart disease.
• Have a prolonged QT interval on an ECG.
• Have a history of lung disease requiring steroids or current lung issues that cannot be ruled out by imaging.
• Have spinal cord compression or active brain metastases.
• Have had multiple primary cancers within the last 3 years, except for certain skin cancers or other curatively treated cancers.
• Have severe allergic reactions to the study drug or similar drugs.
• Have an uncontrolled infection needing IV treatment.
• Have active immune system deficiencies or infections like HIV or hepatitis B/C.
• Have received a live vaccine within 30 days before starting the study drug.
• Have unresolved side effects from previous cancer treatments.
• Are pregnant, breastfeeding, or planning to become pregnant.
• Have significant lung illnesses.
• Have autoimmune or inflammatory disorders.
• Have had a complete lung removal surgery.