Sometimes cancer that starts in one part of your body, known as the primary site, spreads to other parts. That’s because cancer cells can travel, or metastasize, via your bloodstream or lymph system. When those primary cancer cells travel to your lungs, it’s called metastatic or secondary lung cancer. It’s a life-threatening condition. And it’s found in about a third of the people who die from cancer. Cancer can spread to any part of your lungs. And you might have one tumor in one lung or many tumors in both lungs. But most of the time they’re on the edges of your lungs or in the lower lobes.