I have had chest xray and throastic spine mri with no contrast. i have this back pain in my upper back that comes and goes. if i had lung cancer would they have saw anything?

NO: To assess lungs for masses, cancerous or not, need cat scan thorax. Chest xray will consistently miss small potentially curable tumors depending on location in lungs , size and density.Mri of the spine has a limited view of parts of the lungs and you can not rule out the presence of a lung lesion with an MRI of the spine and a chest xray. Mri of the thoracic spine is not used to find lung nodules.

Probably: Most lung cancers show up on chest x-ray unless they are really small in which case a ct scan is better. Mri does not picture the lungs very well. At any rate, lung cancer is almost never painful unless it has spread to bones or other structures. And if you smoke, it is always a good idea to quit.