Solstice Oncology Secures £28m Series C+ to Advance Novel Cancer Therapy

Solstice Oncology UK Limited, a newly formed biotechnology company based in Altrincham, has raised £28m in a Series C+ funding round. The allotment, which took place on February 20, 2026, and was filed on March 11, 2026, brings the company's estimated post-money valuation to £231.2m.

Incorporated in February 2026, Solstice Oncology was established by a syndicate of venture capital investors in partnership with the biopharmaceutical company Harbour BioMed. The business focuses on the research, development, and commercialisation of porustobart, also known as HBM4003. This is a fully human monoclonal heavy chain-only anti-CTLA-4 antibody. Solstice holds the exclusive rights to develop and market the clinical-stage asset globally, outside of Greater China, targeting malignancies such as melanoma, colorectal cancer, and hepatocellular carcinoma.

CTLA-4 is a well-known immune checkpoint target in oncology, but existing therapies are often limited by severe toxicity and adverse side effects. Porustobart is designed to boost the immune system's cancer-killing activity while limiting these toxic responses through an optimised pharmacokinetic profile and enhanced regulatory T-cell depletion in tumour tissues. The drug is currently in Phase II testing, having recently demonstrated a 34.8 percent objective response rate in heavily pretreated patients with metastatic colorectal cancer during trials in China. As a newly incorporated entity, Solstice Oncology currently lists zero employees on its LinkedIn profile and has not yet disclosed revenue or profit metrics.

The £28m Series C+ round represents the initial capitalization of the company following its formation. In late February 2026, Harbour BioMed announced a licensing and equity agreement to spin out the asset into Solstice. As part of the formation, Harbour received an upfront package that included cash and a significant equity stake in the new business, alongside future development and commercial milestones that could reach over £800m. While the specific venture capital investors backing this £28m allotment have