Antitumor Activity of Cabozantinib in Metastatic Adult Ewing Sarcoma: A Case Report.

A 49-year-old male with Ewing sarcoma and bone, pleural, lung and mediastinal lymph node metastasis was treated with cabozantinib after four lines of previous systemic treatments. He responded objectively and subjectively well for 8 months. In this heavily pretreated patient, the daily starting dose of 60 mg had to be reduced to 30 mg because of adverse events. We conclude that treatment with cabozantinib administered in further-line was active in this particular patient with metastatic Ewing sarcoma. The underlying mechanism of action remains unclear. Because of a stable disease on a long-term treatment with pazopanib targeting an anti-angiogenic pathway common to both drugs previously administered in this patient, it is hypothesized that the action of cabozantinib could be ascribed to its action on the non-common receptors AXL and c-Met. The potential of cabozantinib should be further investigated more upfront in this disease either alone or in combination with other systemic treatments.