How would you treat a high-grade undifferentiated round cell sarcoma of left frontal lobe dura with gross residual disease after subtotal resection with a suspicious mildly enhancing contralateral brain parenchymal lesion?

The patient is 45 year old and his EWSR1 rearrangement was negative. This does not completely rule out Ewing's sarcoma per my understanding, but thought to be less likely after outside pathology consultation. CT C/A/P negative. The contralateral lesion measures 0.6 cm and is too deep to biopsy and additional surgery was not recommended with corpus callosum involvement, and the patient is no longer symptomatic.