Phase 1/2a Study of Double-Immune Suppression Blockade By Combining a CSF1R Inhibitor (PLX3397) With An Anti-PD-1 Antibody (Pembrolizumab) To Treat Advanced Melanoma And Other Solid Tumors

The goal of this clinical research study is to learn how PLX3397 and pembrolizumab work
together to affect cancer cells.

PLX3397 is designed to target the receptor for CSF1 (CSF1R). Pembrolizumab is designed to
block the interaction between the receptor PD-1 and molecules that bind PD-1. In this study,
PLX3397 and pembrolizumab are being given together in order to study their combined effects
on patients' immune responses to their tumors. Tumor-specific immune responses have been
shown to kill cancer cells and/or to stop tumors from growing.

Part 1 of the study (dose-escalation phase) will establish the safest dose of PLX3397 to be
given in combination with pembrolizumab. Part 2 of the study (expansion phase) will include
an evaluation of efficacy of this combination in the following tumor types:

- Advanced melanoma: prior anti-PD-1/PD-L1 therapy but never responded

- Advanced melanoma: prior anti-PD-1/PD-L1 therapy and responded but later progressed as
defined by irRECIST while on therapy

- Non-small cell lung cancer

- Ovarian cancer

- Gastrointestinal Stromal Tumor (GIST)

- Squamous cell cancer of the head and neck