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OST-HER2 produced a potential overall survival benefit at 2 years in recurrent, fully resected, pulmonary metastatic osteosarcoma.
Treatment with the off-the-shelf immunotherapy OST-HER2 (OST31-164) led to an improvement in overall survival (OS) compared with historical controls in patients with recurrent, fully resected, pulmonary metastatic osteosarcoma, according to final 2-year OS data from a phase 2b trial (NCT04974008).1
Findings announced by OS Therapies demonstrated that evaluable patients (n = 36) experienced a 2-year OS rate of 75%, exceeding a historical control of 40% (P < .0001). Notably, this population did not include 5 patients lost to follow-up during the study.
Additionally, patients who achieved event-free survival (EFS) of at least 12 months experienced a 2-year OS rate of 100%. Among patients who experienced an EFS event prior to 12 months, the 2-year OS rate was 59%.
"The OS data in this nonrandomized OST-HER2 study is encouraging as the results show it was safe and well-tolerated," Peter Anderson, MD, a pediatric oncologist at Cleveland Clinic Children's Outpatient Center in Ohio and a scientific advisor for OS Therapies, stated in a news release. "New treatments are needed for treating [patients with] metastatic osteosarcoma, so I am hopeful this could become an option in the near future."
Previously reported data showed that the phase 2b trial met its primary end point, with OST-HER2 generating a statistically significant 12-month EFS benefit vs historical controls.2 The 12-month EFS rate was 33% for patients treated with OST-HER2 vs 20% with historical controls (P = .0158).
OST-HER2 features a HER2-bioengineered form of Listeria monocytogenes that is designed to induce a strong immune response against HER2-expressing cancer cells. The therapy is intended to prevent metastasis, delay recurrence, and kill primary tumors expressing HER2—either alone or in combination with approved therapies.
The FDA has previously granted rare pediatric disease designation, fast track designation, and orphan drug designation to OST-HER2. The European Medicines Agency (EMA) has also granted orphan drug and fast track designations to the agent.
The open-label, multicenter, single-arm study enrolled patients 12 to 39 years of age with a body weight of at least 40 kg who had histologically confirmed osteosarcoma with at least 1 instance of disease recurrence in the lungs.3 There was no limit on the number of recurrences to enroll, although patients also needed to meet the following criteria:
Notably, radiographic confirmation of CR was not required, but patients needed to undergo a postoperative CT chest scan.
Other key inclusion criteria comprised a Karnofsky performance status (patients over 16 years of age) or a Lansky performance status (patients under 16 years of age) corresponding to an ECOG performance status of 0 to 2; recovery from acute toxicities associated with prior therapies; and adequate organ function.
Investigators excluded patients with metastatic or recurrent disease; concurrent pulmonary recurrence and local recurrence at the primary tumor site; primary refractory disease with progression of the primary tumor on initial therapy; and central nervous system or any extrapulmonary disease involvement at the time of the most recent recurrence.
OST-HER2 was administered at 1x109 CFU once every 3 weeks for 48 weeks, with 1 cycle comprising 12 weeks. Treatment continued until week 48 or until disease progression, unacceptable toxicity, or other discontinuation criteria were met.
EFS served as the trial’s primary end point. Secondary end points included OS and safety.
"The continued outperformance in OS of OST-HER2 when compared with historical control is exactly what we were hoping for when we started [OS Therapies] in 2018," Paul Romness, MPH, chairman and chief executive officer of OS Therapies, added in a news release.1 "We have had highly productive regulatory meetings with the United Kingdom's Medicines and Healthcare products Regulatory Agency, the United States FDA, and the EMA’s Dutch rapporteur. Representatives of all three regulatory agencies, in various ways, indicated that OS may be an appropriate clinical end point to support a conditional marketing authorization, especially when supported with biomarker data. The rationale for OS combined with biomarkers is largely a result of the compelling data recently published in canine osteosarcoma by researchers at the University of Pennsylvania."
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