One of the 'silent' cancers that are usually well advanced before causing symptoms. I can believe that Upshaw only felt sick for a week before his diagnosis.

Medicine is full of mysterious events. I worked in Neuro ICU for a few years. We would see some patients with brain tumors - tumors that did not start in the brain, but were mets from somewhere else in the body. Usually these tumors come from the lungs, but there were a few cases where the primary tumor was never found.