Yes they can. My hubby didn't even know that he had cancer 'til they were going to take a parotid gland out of his neck and during the pre-op exam they discovered a cancer in his left lung. They sent him to Columbia, Mo. to the cancer center who diagnosed him with stage 4 lung cancer. They gave him 6 months to live at that time. He went on a "protocol" program which consisted of 2 years of chemo at once a week. His cancer has been in remission now for 6 years. But it can happen.