Cambridge, Mass. – September 13, 2026 -- Solstice Oncology has launched with a $225 million Series A financing led by RA Capital Management, with participation from Canaan Partners, Forbion and other investors, to advance a second-generation CTLA-4 antibody into earlier-stage cancer treatment.
Solstice secures $225 million to fund neoadjuvant immuno-oncology program
The clinical-stage company is focused on treating cancer in the neoadjuvant setting, before tumors have hardened resistance to therapy. Its lead candidate, porustobart, is a differentiated, Fc-enhanced CTLA-4 antibody being developed across two clinical indications, including microsatellite-stable (MSS) colon cancer and a second, undisclosed indication.
Phase 2 trial targets stage II-III MSS colon cancer patients starting Q4 2026
The Phase 2 trial will evaluate porustobart in combination with pembrolizumab in the neoadjuvant setting for clinical stage II-III MSS colon cancer, the largest patient segment within colon cancer that has not yet benefited from immunotherapy. Enrollment is set to open early in the fourth quarter of 2026, with data anticipated in the second half of 2027.
Earlier Phase 2 data showed 30% response rate in late-line colorectal cancer patients
Porustobart, discovered and developed by Harbour BioMed (HKEX: 02142) under the internal designation HBM4003, previously demonstrated a 30% objective response rate (7 of 23 patients) in combination with the PD-1 inhibitor tislelizumab among late-line MSS metastatic colorectal cancer patients without liver metastases. The median duration of response reached 8.4 months, with a safety profile the companies describe as favorable.
Harbour BioMed licensed global rights outside Greater China in February 2026
Harbour BioMed entered into a license agreement and equity partnership with Solstice Oncology in February 2026, granting exclusive development and commercialization rights to porustobart outside Greater China. Solstice, founded the same month, filed and cleared an Investigational New Drug application before moving directly into the Phase 2 trial.
"We believe the greatest opportunity in oncology lies in treating disease earlier, in the neoadjuvant setting, when the tumor is still present, the immune system is still intact, and disease hasn't yet hardened its resistance to treatment," said Caroline Loew, PhD, CEO of Solstice Oncology.