DS-8201a in Pre-treated HER2 Breast Cancer That Cannot be Surgically Removed or Has Spread [DESTINY-Breast02]

The study is designed to compare DS 8201a versus standard of care (investigator's choice) in
subjects with unresectable and/or metastatic breast cancer previously treated with T-DM1.

Inclusion Criteria:

- Is the age of majority in their country

- Has pathologically documented breast cancer that:

1. is unresectable or metastatic

2. has confirmed HER2-positive expression as determined according to American
Society of Clinical Oncology - College of American Pathologists guidelines
evaluated at a central laboratory

3. was previously treated with ado-trastuzumab emtansine (T-DM1)

- Has documented radiologic progression (during or after most recent treatment or within
6 months after completing adjuvant therapy)

- Is HER2 positive as confirmed by central laboratory assessment of most recent tumor
tissue sample available. If archived tissue is not available, agrees to provide a
fresh biopsy.

- Male and female participants of reproductive/childbearing potential must agree to use
a highly effective form of contraception or avoid intercourse during and upon
completion of the study and for at least:

1. 4.5 months after the last dose of DS-8201a

2. 6 months after the last dose of lapatinib/capecitabine for female participants (3
months for male participants)

3. 7 months after the last dose of trastuzumab/capecitabine

- Has adequate hematopoietic, renal and hepatic functions

Exclusion Criteria:

- Has previously participated in an antibody drug conjugate study sponsored by Daiichi
Sankyo

- Has had prior treatment with capecitabine

- Has uncontrolled or significant cardiovascular disease

- Has a history of (noninfectious) interstitial lung disease (ILD)/pneumonitis that
required steroids, has current ILD/pneumonitis, or suspected ILD/pneumonitis that
cannot be ruled out by imaging at screening

- Has active central nervous system (CNS) metastases