OS Therapies (OSTX) shares are getting a nice premarket boost Tuesday after the company announced that its Phase 2b trial of OST-HER2 hit a statistically significant survival milestone at the 2.5-year mark. For a small biotech, that's the kind of data that can change the conversation.

The trial enrolled patients with pulmonary metastatic osteosarcoma — a nasty bone cancer that spreads to the lungs. The results showed a 75% survival rate for patients treated with OST-HER2, versus 47% in the historical control group. That difference came with a p-value of 0.003, which is about as statistically significant as it gets in oncology trials.

What's particularly encouraging is that the benefit seems to be holding up over time. At the two-year mark, survival was 75% for the treatment group versus 60% for controls (p = 0.034). The fact that no new deaths occurred between the two-year and 2.5-year timepoints in the treated group suggests the effect is durable.

The company also highlighted a patent-pending pharmacodynamic immune response biomarker signature that was developed as a surrogate endpoint for clinical efficacy. That kind of biomarker can be a big deal for regulators, as it provides a biological readout that correlates with how well the drug is working.

This data isn't just a scientific win — it's a regulatory catalyst. OS Therapies is now gearing up for a series of meetings with drug agencies around the world to map out approval pathways.

The European Medicines Agency (EMA) and Australia's Therapeutic Goods Administration (TGA) have already agreed that three-year overall survival data — expected in early Q4 2026 — will serve as the primary evidence for conditional Marketing Authorization Applications. A rolling review process is already underway in Europe, which could speed things up.

In the U.S., OS Therapies is preparing for a Type B pre-Biologics License Application meeting with the FDA. The goal is to discuss using the upcoming three-year survival data as the basis for a Biologics License Application under the Accelerated Approval Program. That program is designed to get promising drugs to patients faster based on surrogate endpoints.

The company also plans to meet with the FDA in a Type C meeting and separately with the U.K. Medicines and Healthcare products Regulatory Agency (MHRA) through a Scientific Advice Meeting in early June 2026.

For investors, the message is clear: OS Therapies is moving methodically through the regulatory maze, and the data is giving them a stronger hand in those discussions. Shares were up 8.29% at $2.03 in premarket trading Tuesday.