Cancers that can spread from their original locations are called secondary cancers. This process, called metastasizing, moves the cancers through the bloodstream, lymphatic system, or by direct extension to a new location. One or many of the cancerous cells of the primary cancer (where the disease originated) can break off and slip into the bloodstream or lymphatic system to reach other organs.
Cancerous cells in the lungs as well can appear there without having originated there; in children, cancers of the lungs usually manifest through this process. Cancer that appears in the lungs but did not originate there is called secondary lung cancer. Even though it affects the lungs, secondary lung cancer is named according to the type of cancer it originated from, the primary cancer. For example, breast cancer that spreads to the lungs and becomes secondary lung cancer would still be considered breast cancer.
While nearly every type of cancer has the ability to metastasize and spread to the lungs, some do so more commonly than others. Secondary lung cancer is usually a result of bladder, breast, prostate, or colon cancer. Sarcoma, Wilms tumor and neuroblastoma also tend to migrate to the lungs.