Phase 1/2a Dose Escalation and Expansion Study Evaluating Safety, Tolerability, Pharmacokinetic, Pharmacodynamics and Anti-Tumor Activity of PF-06873600 as a Single Agent and in Combination with Endocrine Therapy

The purpose of this clinical trial is to learn about the safety and effects of study medicine
(PF-06873600) when taken alone or with hormone therapy by people with cancer.

People may be able to participate in this study if they have the following types of cancer:
Hormone Receptor positive (HR+) breast cancer; Human Epidermal Growth Factor Receptor 2
(HER2)-negative breast cancer that is advanced or metastatic (spread to other parts of the
body); triple negative breast cancer; epithelial ovarian cancer; fallopian tube cancer; or
primary peritoneal cancer.

All participants in this study will receive the study medicine by mouth, 1 to 2 times a day
at home. The dose of the study medicine may be changed during the study.

Some participants will also receive hormone therapy. The hormone therapy will be either
letrozole by mouth once a day at home, or fulvestrant as a shot into the muscle. Fulvestrant
will be given every two weeks at the study clinic for the first month, and then once a month
after that.

Participants will take part in this study for at least 7 to 8 months, depending on how they
respond to the therapy. During this time participants will visit the study clinic once a
week.

Inclusion Criteria:

- Have a diagnosis of Hormone Receptor Positive (HR+), Human Epidermal Growth Factor
Receptor 2 Negative (HER2-) breast cancer

• Prior combined CDK 4/6 inhibitor and endocrine therapy and 1 or 2 prior lines of
chemotherapy

- Have a diagnosis of metastatic triple negative breast cancer (TNBC)

• Up to 1-2 prior lines of chemotherapy

- Have a diagnosis of advanced platinum resistant epithelial ovarian cancer
(EOC)/fallopian tube cancer/primary peritoneal cancer (PPC)

• Up to 2-3 prior lines of therapy

- Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) 0 or 1

- Measurable disease or non-measurable disease and refractory to or intolerant of
existing therapies (Part 1)

- Measurable disease as defined by RECIST 1.1 is required (Part 1B and Part 2 only)

Exclusion Criteria:

- Known active uncontrolled or symptomatic Central Nervous System (CNS) metastases

- Other active malignancy within 3 years prior to randomization, except for adequately
treated basal cell or squamous cell skin cancer, or carcinoma in situ

- Major surgery or radiation within 4 weeks prior to study entry

- Last anti-cancer treatment within 2 weeks prior to study entry

- Participation in other studies involving investigational drug(s) within 4 weeks prior
to study entry

- Pregnant or breastfeeding female patients

- Active inflammatory gastrointestinal (GI) disease, known diverticular disease or
previous gastric resection or lap band surgery including impairment of gastro
intestinal function or GI disease