What are the mechanims by which a cancer can compress the spinal cord?

1. Cancer metastasizes to a vertebral body which subsequently erodes and encroaches on the spinal cord (most common mechanism).
2. A cancer occupying the paraspinous space may enter the spinal canal through the intervertebral foramen and subsequently cause cord compression.
   
3. Cancer occurs directly at the spinal cord or meninges.
   

Source

Halfdanarson, T. et al. "Oncologic Emergencies: Diagnosis and Treatment" Mayo Clin Proc. 2006 June (LLSA Readings 2009)