The off-the-shelf immunotherapy OST-HER2 (OST31-164) demonstrated impressive 2-year overall survival results in a phase 2b trial for patients with recurrent, fully resected pulmonary metastatic osteosarcoma. The 2-year overall survival rate reached 75% among evaluable patients (n=36), significantly higher than the historical control rate of 40% (P<.0001). Patients who achieved an event-free survival (EFS) of at least 12 months had a 100% 2-year overall survival rate. The study had previously met its primary endpoint, showing a statistically significant 1-year EFS rate of 33% compared with 20% in historical controls (P=.0158).
OST-HER2 is a HER2-bioengineered form of Listeria monocytogenes designed to stimulate a strong immune response against HER2-expressing cancer cells to prevent metastasis, delay recurrence, and eradicate residual tumor cells.
The open-label, single-arm phase 2b trial enrolled patients aged 12 to 39 years with histologically confirmed osteosarcoma that had recurred in the lungs and was fully resected prior to enrollment. Participants received OST-HER2 at 1×10⁹ CFU once every 3 weeks for up to 48 weeks.
OST-HER2 has received rare pediatric disease, fast track, and orphan drug designations from the FDA, as well as similar designations from the EMA. Given the encouraging overall survival and biomarker data, the developers are pursuing conditional marketing authorization.