Does cancer generally spread from original tumors to other parts of the body, or does it just start in other parts of the body on it’s own without help from the other tumor? Which is more likely?
Cancer commonly spreads from the original tumor. Called metastasis.
It is possible for two types of cancer to pop up. So a smoker could have lung cancer and an oral cancer due to smoking, but they have each developed independently.
More likely is that an advanced cancer (generally Stage III or IV) will metastasize and spread in the body. In this case, you might have lung cancer that has spread to the liver. It is not liver cancer. The cancer cells in the liver will be lung cancer cells.
I asked a related question on here a few months ago. If doctors find tumors in two different locations — say, the breast and the liver — how do they determine which cancer was original? The answer was that each kind of original cancer produces distinct cells of its own. So if your cancer originated in the breast, doctors would find breast cancer cells in both the breast and the liver, which is how they would know that it was breast cancer that had spread to another organ.