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StocksMediumUpdated•Originally published 8 September 2026•Updated 8 September 2026•
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OS Therapies Reports 71.2% 3-Year Survival for OST-HER2 Versus 45.8% Historical Control

Key Facts

1OST-HER2's 3-year overall-survival rate was 71.2% versus 45.8% for a combined published historical control, at p=0.002.
2The trial enrolled 41 patients, with 2 yet to reach the 3-year timepoint and 6 lost to follow-up at the interim analysis.
3The Phase 2b trial was single-arm and used a historical comparison rather than a concurrent control arm.

OS Therapies said an interim analysis from its Phase 2b OST-HER2 trial showed a 71.2% 3-year overall-survival rate, versus 45.8% for a combined published historical control. The company reported that the difference was statistically significant at p=0.002.

The analysis covers patients with fully resected pulmonary metastatic osteosarcoma. The trial enrolled 41 patients; 2 had not yet reached the 3-year timepoint when the data were announced, while 6 were lost to follow-up, leaving the readout interim.

The Phase 2b study tested whether OST-HER2 could prevent or delay recurrence. It was a single-arm study and was not designed as a randomized controlled trial, so outcomes were compared with published historical data rather than patients enrolled concurrently in a control arm.

OST-HER2 is an investigational off-the-shelf immunotherapy built from a genetically modified, attenuated strain of Listeria monocytogenes that expresses HER2 peptides, with the aim of prompting an immune response against HER2-expressing cancer cells.

The survival figures provide a positive clinical signal for the OST-HER2 program, but the single-arm design and reliance on a historical comparison limit conclusions that OST-HER2 alone caused the difference. Statistical significance in this analysis also does not amount to regulatory approval or guarantee later-stage success.

The company said it plans to complete the final analysis within a month and hold an FDA statistical-methods meeting in mid-September 2026. It is also targeting regulatory submissions in Q4 2026 and the start of a confirmatory Phase 3 trial in the U.K.; the final data and regulators' responses are the program's next major tests.