DS-8201a in Human Epidermal Growth Factor Receptor2 (HER2)-Expressing Colorectal Cancer

At study start, only Cohort A is active.

If, and when, Cohort B and C become active depends on the assessment of benefit and risk
observed in the program.

The sponsor will inform the investigators if, and when, Cohort B and C are active.

Inclusion Criteria:

- Has pathologically documented unresectable, recurrent, or metastatic colorectal
adenocarcinoma (until sponsor's notification to the study sites, subject must be a
RAS/BRAF wild-type cancer)

- Has received at least 2 prior regimens of standard treatment

- Has measurable disease assessed by the investigator based on RECIST version 1.1.

- Has an Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 to 1

Exclusion Criteria:

- Has a medical history of myocardial infarction within 6 months, symptomatic congestive
heart failure

- Has a medical history of clinically significant lung disease

- Has spinal cord compression or clinically active central nervous system metastases,
defined as untreated and symptomatic, or requiring therapy