Harbour BioMed partner Solstice Oncology secures US$225M to target MSS colon cancer

CHINA—Harbour BioMed’s partner Solstice Oncology has raised US$225 million in a Series A financing round to advance porustobart, an investigational immuno oncology therapy for cancer treatment.

RA Capital Management led the financing, with participation from Forbion, Canaan Partners, and other investors.

Solstice Oncology will use the funding to advance porustobart, with an initial focus on treating patients with microsatellite stable (MSS) stage II and III colon cancer before surgery.

Harbour BioMed developed porustobart as a second-generation, Fc-enhanced antibody targeting cytotoxic T lymphocyte-associated protein 4 (CTLA 4), an immune checkpoint involved in regulating the body’s immune response to cancer.

The company is investigating the therapy in two indications.

However, its initial development will focus on MSS colon cancer, which accounts for most colon cancer cases and has limited benefit from currently approved immunotherapies.

Phase II trial planned for 2026

Solstice Oncology plans to begin enrolment in a Phase II clinical trial of porustobart in combination with pembrolizumab in the fourth quarter of 2026.

The study will assess the combination as a neoadjuvant treatment, meaning patients will receive the therapy before surgery.

Researchers will evaluate whether combining the two immunotherapies can improve treatment outcomes for patients with MSS colon cancer.

The approach targets an area of significant unmet need because MSS tumours generally respond poorly to existing immune checkpoint therapies.

Harbour BioMed and Solstice Oncology established their partnership in February 2026 through a licence and equity agreement.

Under the agreement, Solstice Oncology received exclusive rights to develop and commercialize Porustobart outside Greater China.

Harbour BioMed identifies the antibody as HBM4003 in its development pipeline.

Earlier clinical data support further development

Previous clinical research conducted by Harbour BioMed evaluated porustobart in combination with the PD 1 inhibitor tislelizumab in patients with MSS metastatic colorectal cancer who did not have liver metastases.

The Phase II study produced an objective response rate of 30%, with seven of 23 patients responding to treatment.

The median duration of response was 8.4 months, while researchers reported a favourable safety profile for the combination.

Harbour BioMed said these findings will support further studies of porustobart with PD 1 or PD-L1 inhibitors in patients with earlier-stage disease.

Harbour BioMed founder, chairman and chief executive officer Dr Jingsong Wang said the company was pleased to see Solstice Oncology launch with strong backing from investors and advance porustobart into the neoadjuvant setting.

Wang added that Harbour BioMed, as the antibody’s originator and a Solstice partner, would continue supporting its development and evaluating its potential in patients worldwide.

Meanwhile, in November 2025, Harbour BioMed and Evinova China established a collaboration to apply artificial intelligence and digital technologies to biologics development.

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