What would cancer look like in an X-ray of the spine?

Very Variable. It may not be detectable on an x-ray or could mimic another process like an infection or trauma. 2 classic presentations are called blastic or lytic- blastic appearance is when the region affected appears denser and lytic is when the affected region looks as if someone took n eraser to the area ; looks less dense. There are other image studies such as a bone scan or MRI that can help deliniate.
Several. There are several possibilities. It might not show up at all and the x-ray could be normal. There could be simple demineralization of bone. There can be destruction of certain processes of vertebra (e). There could be "punched out" holes, or there could be too much mineralization (osteoblasts lesions).