Solstice Oncology launched this week with $225 million in Series A financing to advance an antibody therapy designed to treat cancer earlier — before surgery rather than after it has spread — betting that timing, not just biology, can improve outcomes for solid tumors.
The round was led by RA Capital Management, with Canaan Partners and Forbion also participating. The Boston-based company, founded in February, licensed its lead drug — porustobart, a second-generation, Fc-enhanced antibody targeting the CTLA-4 immune checkpoint — from China's Harbour BioMed in a deal that included a $105 million upfront payment for development and commercialization rights outside Greater China.
Porustobart is designed to block CTLA-4 while also depleting regulatory T cells that would otherwise suppress the immune system's attack on tumors. In an earlier-stage trial combining the drug with the PD-1 inhibitor tislelizumab in patients with late-line, microsatellite-stable metastatic colorectal cancer, the combination produced a 30% objective response rate with a median duration of 8.4 months, according to the company. Solstice now plans to move the drug into the neoadjuvant setting, pairing it with Merck's Keytruda ahead of surgery in patients with stage II and III colon cancer; a Phase 2 trial is set to open enrollment in the fourth quarter, with data expected in the second half of 2027.
We believe the greatest opportunity in oncology lies in treating disease earlier, in the neoadjuvant setting, when the tumor is still present.
Caroline Loew, Chief Executive Officer, Solstice Oncology
Harbour BioMed founder and chief executive Dr. Jingsong Wang said he was "pleased to see Solstice Oncology launch with strong support from leading investors" as the drug moves into its next phase of testing.
A crowded field for early money
The raise adds to a steady flow of venture money into immuno-oncology this year, as investors bet that combining checkpoint inhibitors earlier in the treatment timeline — rather than only after a cancer has become metastatic — could open a meaningfully larger and more durable market than late-line therapy alone.
At $225 million, Solstice's Series A ranks among the largest opening rounds in oncology this year, reflecting both the size of the licensing commitment behind porustobart and investors' appetite for later-stage biotech bets that come with existing human efficacy data attached, rather than purely preclinical science. The company has not disclosed a timeline for further fundraising, saying only that the current round is intended to fund the Phase 2 program through its readout.