Prolonged clinical response is possible with regorafenib in refractory osteosarcoma: A case report

<b>Background:</b> Treatment options for metastatic unresectable osteosarcoma are limited, and there is no standard approach after the failure of first-line chemotherapy. Conventional chemotherapy in the second and subsequent lines typically yield a median progression-free survival (PFS) of less than 4 months, with objective response rates ranging from 3 to 29%. The activity of anti-vascular endothelial growth factor receptor multi-tyrosine kinase inhibitors (TKIs) in bone sarcomas has been demonstrated. We present a case of metastatic osteosarcoma exhibiting a durable response to regorafenib treatment.<br /> <b>Case: </b>We discuss a 30-year-old male with metastatic osteosarcoma who had extensive bone and lung metastases and was ineligible for metastasectomy. The patient had received all active chemotherapy regimens in the early and metastatic stages except ifosfamide. Next generation sequencing analysis of resected tumor tissue revealed a possibly pathogenic missense mutation (P.G472E) in NOTCH1 gene. Due to the presence of heart failure with a reduced ejection fraction, chemotherapy was not considered, and regorafenib was initiated. After four cycles of regorafenib, a partial metabolic response was achieved. The patient was followed up without progression under regorafenib for 15 months, without requiring dose reduction. Unfortunately, the treatment had to be interrupted for an extended period due to challenges with recurrent tumor infection and the necessity for repeated surgeries. Following successful wound site control, we restarted full-dose regorafenib and achieved a metabolic partial response again.<br /> <b>Conclusion: </b>To our knowledge, this case represents the longest achieved PFS with regorafenib in metastatic osteosarcoma. TKIs can provide a durable clinical response in metastatic osteosarcoma patients. Clinical and molecular biomarkers are required to determine which patients are most likely to benefit from these treatments.