Can someone live years without ever knowing they have stage iv lung cancer or kidney cancer ?. and only to find out later on during an autopsy that it was present ?

Yes: Both are cancers in deep tissue and may cause no symptoms until coughing, bleeding, pain.

Unlikely: It is more likely that the person developed cancer in the past few months or years and it was never diagnosed. Still, anything is possible.

Depends: It depends on the type of lung or kidney cancer. Most types of lung cancer are very aggressive and grow very fast -- it would be unusual 2 have them very long before it became obvious (and deadly). If one of these were found on autopsy it most likely began closer to the time the patient died. Stage 4 implies that the cancer has already spread and this would be toward the very end of the disease.

Unlikely: If someone has stage IV lung or kidney cancer, going to have symptoms sooner rather than later. Hope this helps.