Lung cancer is a tricky disease to treat because most people don't find out they have it until it has already spread to other parts of the body. This means that even surgery is sometimes not effective in removing all of the cancer cells from a person's body.
The three main methods of treating cancer are:
surgery (if cancer is found in only one lung)
radiation therapy (using x-rays to kill cancer cells)
chemotherapy (using drugs to kill cancer cells)