Study of Vadastuximab Talirine (SGN-CD33A; 33A) in Combination With Azacitidine in Patients With Previously Untreated Higher Risk MDS

In the phase 1 portion of the study, escalating doses of 33A will be evaluated in combination
with azacitidine, and a dose of 33A will be selected to proceed to phase 2. The phase 2
portion of the study is randomized, double-blind and placebo-controlled; it is designed to
compare the overall response rate (ORR) between 2 study arms.

Inclusion Criteria:

- Subjects with cytologically/histologically confirmed MDS according to the World Health
Organization (WHO) 2008 classification.

- Previously untreated for Myelodysplastic Syndrome (MDS)

- Age ≥18 years of age.

- Eligible for therapy with azacitidine.

- Life expectancy of at least 12 weeks.

- Eastern Cooperative Oncology Group (ECOG) performance status ≤2.

- Adequate baseline laboratory parameters.

Exclusion Criteria:

- Received prior treatment for MDS with lenalidomide or hypomethylating agents (HMAs).

- History of one of the following myeloproliferative neoplasms: essential
thrombocythemia, polycythemia vera, and primary myelofibrosis.

- Second malignancy currently requiring active therapy (except for
hormonal/anti-hormonal treatment, eg, prostate or breast cancer).

- Candidates for allogeneic stem cell transplant at the time of screening.