Safety and Efficacy of SGN-LIV1A Plus Pembrolizumab for Patients With Locally-Advanced or Metastatic Triple-Negative Breast Cancer

The primary goal of this study is to evaluate the combination of SGN-LIV1A, which targets
LIV-1- expressing tumor cells, with the checkpoint inhibitor pembrolizumab for patients with
unresectable locally-advanced or metastatic triple-negative breast cancer. These two drugs
act through distinct and possibly complementary modes of action.

This is a single-arm, open-label, multicenter trial. Patients given SGN-LIV1A and
pembrolizumab in Part A will be monitored for frequency of dose-limiting toxicities to
determine a recommended phase 2 dose for expansion in Part B. In addition to safety measures,
objective response rate, progression-free survival, overall survival, and other efficacy
outcomes will be assessed.

Inclusion Criteria:

- Metastatic or locally-advanced, histologically documented TNBC (absence of HER2, ER,
and PR expression)

- Have not previously received cytotoxic therapy for the treatment of unresectable
locally-advanced breast cancer or metastatic breast cancer

- At least 6 months since prior treatment with curative intent and recurrence

- At least 1 tumor 10mm in diameter or greater OR lymph node of at least 15 mm in short
axis

- ECOG performance status of 0 or 1

- Able to provide biopsy tissue for biomarker analysis

- Meet baseline laboratory data criteria

- Not pregnant. Must agree not to become pregnant until at least 6 months after ceasing
study treatment

Exclusion Criteria:

- Prior immune-oncology therapy

- Pre-existing neuropathy of at least Grade 2

- History of carcinomatous meningitis or active central nervous system (CNS) metastases.
Patients are eligible if CNS metastases are adequately treated and patients have
neurologically returned to baseline (except for residual signs or symptoms related to
the CNS treatment) for at least 4 weeks prior to enrollment. Patients must be off
corticosteroids.

- Received prior radiotherapy within 2 weeks of start of study treatment or have not
adequately recovered from prior radiotherapy

- Active autoimmune disease requiring systemic treatment within the past 2 years

- History of interstitial lung disease

- Current pneumonitis or history of pneumonitis requiring steroids