Tislelizumab

Building on a licensing agreement signed in February, Solstice Oncology has pulled in $225 million in series A funding to usher its anti–CTLA-4 antibody porustobart into a Phase II study for microsatellite-stable (MSS) colon cancer. The financing was led by RA Capital Management and joined by Canaan Partners, Forbion and other investors. "We believe the greatest opportunity in oncology lies in treating disease earlier, in the neoadjuvant setting, when the tumour is still present, the immune system is still intact, and disease hasn't yet hardened its resistance to treatment," said CEO Caroline Loew.Porustobart, which originated at Harbour BioMed, is designed to overcome multiple facets of immunosuppression through two mechanisms of action: CTLA-4 checkpoint blockade and regulatory T-cell (Treg) depletion via antibody-dependent cellular cytotoxicity. The mid-stage study will evaluate porustobart in combination with Merck & Co.'s PD-1 inhibitor Keytruda (pembrolizumab) in the neoadjuvant setting for MSS clinical stage II-III colon cancer.According to Solstice, the two agents are expected to work synergistically. Keytruda will reawaken T-cells that have already recognised the tumour, while porustobart widens that response by releasing a second, independent brake on the immune system and depleting the immunosuppressive Tregs that shield tumours from attack. In an earlier Phase II study conducted by Harbour BioMed, porustobart in combination with BeOne Medicines' PD-1 inhibitor Tevimbra (tislelizumab) showed a 30% objective response rate and an 8.4-month median duration of response in late-line MSS metastatic colorectal cancer patients without liver metastases."Treating patients early with an immuno-oncology combination therapy…could allow the immune response to act systemically, reaching micrometastatic disease well beyond the primary tumour, which is where we see the greatest opportunity to improve cure rates and long-term survival," Loew explained.The company noted that MSS colon cancer has historically been unresponsive to immunotherapy, but data for new Fc-enhanced CTLA-4 molecules, such as porustobart, seem to suggest clinical synergistic effect with PD(L)-1 blockade. Solstice is also hoping that porustobart's shorter half-life versus first-generation CTLA-4 antibodies will enable more flexible dosing, potentially reducing the frequency and duration of immune-related adverse events, often seen as a key limiting factor for its precursors.Enrolment in porustobart's Phase II study is expected to start in the fourth quarter, with data due in the second half of 2027.Beyond MSS clinical stage II-III colon cancer, the biotech has hopes for the drug in the neoadjuvant setting across multiple tumour types. Porustobart is currently also under development in a second, undisclosed indication.

iStock, Oksana Nazarova Solstice Oncology, founded in February, is emerging from stealth having already secured an investigational new drug application from the FDA for a Phase 2 trial of a CTLA-4 antibody purchased from China’s Harbour BioMed. A new cancer biotech has dawned as Solstice Oncology launches with a massive $225 million Series A fundraising that will be used to advance a CTLA-4 antibody from China’s Harbour BioMed. Solstice CEO Caroline Loew said the mission will be to address cancer sooner, in the pre-surgical neoadjuvant setting when the tumor is present but the immune system is still working to keep it at bay and the patient has not yet been exposed to other treatments. At the center of the new biotech is porustobart, which has the FDA’s greenlight to be tested in a Phase 2 trial for neoadjuvant advanced colon cancer plus another undisclosed indication, according to a Wednesday release. Enrollment for the study, which will pair porustobart with Merck’s Keytruda, will begin in the fourth quarter, Solstice said. Data are expected to arrive in the second half of 2027. “Treating patients early with an immuno-oncology combination therapy like the one we are evaluating in our Phase 2 trial could allow the immune response to act systemically, reaching micrometastatic disease well beyond the primary tumor, which is where we see the greatest opportunity to improve cure rates and long-term survival,” Loew said in a statement. IPO Biotech IPOs approach ‘escape velocity’ barring yellow flags that could threaten rebound Twenty-five biotechs have used the IPO route to go public this year—with five of those debuts occurring this month alone. It’s the most IPOs since 2021, when the industry recorded 78 during the height of the COVID-19 pandemic. August 25, 2026 · 3 min read · Gabrielle Masson Read more Solstice was founded in February and moved quickly to prep porustobart for clinical trials. The therapy is intended to be used in combination with a checkpoint inhibitor such as Keytruda to awaken the body’s immune system and then target the cancer. Colon cancer has not typically responded to this approach, but the next-generation CTLA-4 antibodies may have better performance, according to Solstice. The biotech noted that porustobart has a short half-life, which could allow more flexible dosing and a better safety pro previous CTLA-4 therapies. The drug was licensed by Solstice’s investors from China’s Harbour for about $105 million at signing, including a $50 million upfront payment, $5 million near-term cash and a $50 million equity stake in the biotech, according to a February press release from the Chinese company. Harbour could also potentially receive up to $1.1 billion in commercial milestones down the road based on ex-China sales. Harbour has already tested porustobart in Phase 1b trials of patients with late-line colon cancer paired with BeOne Medicine’s checkpoint inhibitor Tevimbra. The early results showed a 30% objective response rate, or 7 out of 23 patients, with a median duration of response of 8.4 months. Solstice’s Series A financing was led be RA Capital Management, known for biotechs such as Blueprint Medicines, Global Blood Therapeutics and KalVista Pharmaceuticals—all of which were ultimately acquired. Canaan Partners, Forbion and other investors also joined the round.