A 58-year-old man with a 3-year history of metastatic prostate cancer presents to the emergency department with progressive lower back pain for 2 weeks, worse at night and with Valsalva maneuver. Over the past 3 days, he has developed symmetric proximal lower-extremity weakness and a band-like sensory loss at the T8 level. MRI of the whole spine shows a hypointense vertebral body lesion at T7 with posterior epidural soft-tissue extension. The structure marked **C** in the diagram demonstrates cord compression with associated T2 hyperintensity. Which of the following is the most appropriate IMMEDIATE management step?