Summary
A medRxiv preprint describes retrospective records for 57 osteosarcoma patients given mifamurtide through access programmes at Memorial Sloan Kettering Cancer Center. Outcomes differed by disease setting, and the authors reported no serious adverse events considered possibly or probably related to the drug.
A retrospective study of 57 people treated with mifamurtide for osteosarcoma at Memorial Sloan Kettering Cancer Center (MSK) reports that the drug could be administered through expanded-access and compassionate-use pathways in the United States. The medRxiv preprint describes differing progression-free and overall survival estimates across patient groups, alongside the authors’ report that no serious adverse events were considered possibly or probably related to mifamurtide.
The records covered patients treated at MSK from 2016 to 2026. Mifamurtide, also called liposomal muramyl tripeptide phosphatidylethanolamine (L-MTP-PE), is approved for osteosarcoma in many countries but, according to the study, was not available for routine use in the US. The median patient age was 14 years, with a range of 2 to 60. At diagnosis, 72% had localized disease and 28% had metastatic disease.
Treatment and reported outcomes
Patients received mifamurtide at 2 mg per square metre intravenously twice a week for 12 weeks, followed by weekly treatment for 24 weeks. The researchers assessed outcomes according to treatment setting and, for patients treated upfront, metastatic status and the amount of tumour necrosis—the proportion of tumour tissue that had died—after resection.
Among five patients with localized disease and at least 90% necrosis at resection, no events were reported; progression-free survival (PFS) and overall survival (OS) were both 100% at a median follow-up of 29 months.
For 22 patients with localized disease and less than 90% necrosis who received mifamurtide upfront, reported PFS was 82% at 12 months, 66% at 24 months and 59% at 48 months. OS was 95% at 12, 24 and 60 months. Among eight patients with metastatic disease treated upfront, PFS was 73%, 58% and 39% at 12, 24 and 36 months, respectively; OS was 100%, 86% and 86% at those intervals.
The group treated after relapse included 22 patients. Their PFS was 34% at 12 months, 23% at 24 months and 17% at 36 months. OS was 91% at 12 months, 70% at 24 months and 35% at 60 months.
The authors reported no new grade 3–4 safety signals. These findings describe outcomes in distinct groups with different disease histories; the survival estimates should not be read as a direct comparison between those groups.
What the study can tell clinicians
The report adds a US single-centre account of how mifamurtide was administered outside routine availability, and documents outcomes in a real-world clinical setting. The authors characterize administration as feasible and safe, while noting the study’s single-institution setting, patient heterogeneity and use of expanded-access and compassionate-use pathways.
This was a retrospective review, not a randomized comparison. The abstract provides no untreated comparison group, so the reported survival rates cannot isolate mifamurtide’s effect from other differences among patients or their care. The study is a preprint, and its subgroup estimates come from small numbers, including just five patients in the localized, high-necrosis group.