G1T48, an Oral SERD, in ER-Positive, HER2-Negative Advanced Breast Cancer

Inclusion Criteria:

- For Part 1, postmenopausal women only

- For Part 2, any menopausal status

- Confirmed diagnosis of ER-positive, HER2-negative advanced breast cancer, not amenable
to curative therapy

- For Part 1, prior treatment with less than 4 prior lines of chemotherapy

- For Part 2, prior treatment with less than 2 prior line of chemotherapy

- Prior treatment with less than 4 prior endocrine therapies for metastatic breast
cancer

- Patients must satisfy 1 of the following criteria for prior therapy:

- Progressed during treatment or within 12 months of completion of adjuvant therapy
with an aromatase inhibitor

- Progressed after the end of prior aromatase inhibitor therapy for
advanced/metastatic breast cancer

- For Part 1, evaluable or measurable disease

- For Part 2, measurable disease as defined by RECIST, Version 1.1 including bone-only
disease

- ECOG performance status 0 to 1

- Adequate organ function

Exclusion Criteria:

- Prior treatment with SERMs or SERDs within 5 weeks of first G1T48 dose

- Active uncontrolled/symptomatic CNS metastases, carcinomatous meningitis, or
leptomeningeal disease

- Anticancer therapy within 14 days of first G1T48 dose or within 28 days for
antibody-based therapy

- Concurrent radiotherapy, radiotherapy within 14 days of first G1T48 dose, previous
radiotherapy to the target lesion sites, or prior radiotherapy to > 25% of bone marrow

- Prior hematopoietic stem cell or bone marrow transplantation