Why is secondary lung cancer common?

Secondary lung cancer is when a cancer that started somewhere else in the body has spread to the lung.

Where a cancer starts is called the primary cancer. This is when some cancer cells break away from the primary cancer. They can move through the bloodstream or lymph system to another part of the body to form a new tumor. This is called a secondary cancer. Secondary cancers are also called metastases  The secondary cancer is made of the same type of cells as the primary cancer.

If your cancer started in your bowel and has spread to your lung, the areas of cancer in the lung are made up of bowel cancer cells.  

This is different from having a cancer that first started in the lung (a primary lung cancer). In that case, the cancer is made up of lung cells that have become cancerous.

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