Bones, lungs, and the liver are the most common places for cancer cells to spread, or "metastasize."
Once in the bone, these cancer cells can form new metastatic tumors. Do you then have bone cancer? No. You still have the type of cancer you were diagnosed with, except now it is metastatic. For example, breast cancer that spreads is known as "metastatic breast cancer." Metastatic cancers in the bone are also called bone metastases, or bone "mets."
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About three out of four cases of bone metastasis result from tumors in the breast, prostate, lung, or kidney. Almost 70% of people with advanced breast or prostate cancer have bone metastasis; bone is commonly the first area of metastasis for these cancers.
How and Why Cancers Metastasize to Bones
The spread of cancer to bone is a complex process that doctors are just beginning to understand. Metastasis typically involves the following process:
Cancer cells invade normal tissue nearby, then move through the walls of nearby lymph or blood vessels and begin circulating through the lymphatic system and bloodstream to reach other parts of the body. After stopping in small blood vessels at a further location, they invade the blood vessel walls and migrate into surrounding tissue where they multiply and form smaller tumors. Those new tumors need a blood supply for continued growth, so they stimulate the growth of new blood vessels.
Once they've reached the bone, cancer cells must avoid attacks from the body's immune system. So they may go through more changes. This means the new tumor may be somewhat different from the primary tumor. This can make it more difficult to treat.
Why and Where Tumors Form in Bones
The type of cancer may have something to do with why tumors form in bones. Certain cancers may release proteins that affect how a tumor forms.