Regorafenib in Pediatric Patients With Advanced Osteosarcoma: A Case Series from a Single Institution

Pediatric osteosarcoma is a rare and aggressive malignancy with limited treatment options in cases of progression or metastasis. Regorafenib is an oral multikinase inhibitor targeting vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR), and other kinases, currently approved in Japan for certain gastrointestinal cancers. Its clinical use in osteosarcoma, especially in pediatric patients, has not been well established.

We retrospectively analyzed six pediatric patients with advanced osteosarcoma who were treated with regorafenib at our institution. All patients had previously received standard treatment, including neoadjuvant and adjuvant chemotherapy as well as surgery, and were considered to have disease progression or resistance prior to regorafenib administration. Clinical background, treatment response, adverse events, and progression-free survival (PFS) were evaluated. Tumor response was assessed using RECIST criteria, and adverse events were graded according to CTCAE v5.0.

The average age was 16 years (range=12-18 years), and all patients had received prior surgery and chemotherapy. Regorafenib was administered at adult equivalent doses, with dose reductions required in 3 of 6 patients. Four patients (66.7%) achieved stable disease for at least eight weeks. The longest PFS exceeded 12 months. Common toxicities included diarrhea and hematuria; no grade ≧3 adverse events were observed. All patients underwent genomic testing to guide treatment planning.

This case series suggests that regorafenib may provide disease control with acceptable safety in pediatric patients with advanced osteosarcoma. Further studies are needed to evaluate its efficacy and tolerability in this population as well as in adult patients.