A First-in-human Study of PRTH-101 Monotherapy +/- Pembrolizumab in Subjects With Advanced Malignancies

The goal of this Open-Label Study is to evaluate the safety and tolerability of PRTH-101 alone or in combination with pembrolizumab in adults with advance or metastatic solid tumors. PRTH-101 is a therapeutic antibody that specifically binds to and blocks DDR1, a protein expressed on tumor cells that binds collagen to make a minimally permeable physical barrier that blocks immune cells from interacting with and attacking tumor cells. These "immune cell-excluded" solid tumors are resistant to attack by the immune system (as well as other existing therapies). By disabling DDR1, the collagen fibers lose alignment and loosen, creating gaps in the tumor barrier, thus allowing T-cells to enter and naturally attack the tumor. The main question\[s\] it aims to answer are: * to evaluate the safety and tolerability of PRTH-101 as mono therapy and in combination with pembrolizumab, * to determine the recommended Phase 2 dose as mono therapy and in combination with pembrolizumab, * to evaluate anti-tumor activity of PRTH-101 as mono therapy and in combination with pembrolizumab in selected indications