Solstice Oncology Secures $225 Million for Clinical Trials of CTLA-4 Antibody
Boston-based biotech startup Solstice Oncology has raised $225 million in a Series A round to fund clinical trials of an experimental CTLA-4 antibody called porustobart. The company plans to use this new capital to advance porustobart into a Phase II trial in combination with Merck's PD-1 inhibitor Keytruda, starting with enrollment in the fourth quarter of 2026 and data expected by the second half of 2027.
Porustobart is designed to make microsatellite-stable colon cancer responsive to immunotherapy. Solstice CEO Caroline Loew stated that 'we know that an anti-PD-L1 by itself has a 0% response rate in this setting,' but porustobart combined with a PD-1 inhibitor produced a 30% objective response rate in MSS metastatic colorectal cancer patients without liver metastases.
The company's focus is on the neoadjuvant setting, administering the therapy before surgery when the patient's immune system remains intact and can still recognize the tumor. Loew believes that eradicating micrometastatic disease at this stage 'is where you drive cure.'