How Cancer Spreads (Metastasis)

Overview

Cancer can spread from where it started — the primary site — to other parts of the body. Cells break away from the tumor and travel through the bloodstream or the lymph system. This process is called metastasis.

How Cancer Cells Reach New Places

To spread, cancer cells must:

• Escape the first tumor and grow into the tissue around it.
• Attach to the wall of a nearby blood vessel or lymph vessel, get through it, and travel along it to a new organ or lymph node.
• Stop there, get through the vessel wall again, and move into the new tissue.
• Find a way to grow in the new place, including making new blood vessels to feed it (angiogenesis).
• Avoid being destroyed by the immune system.

Cancer can also affect nerves. Cancer cells can enter the outer covering of a nerve (the sheath) and spread along it, toward the skin or deeper into the body. This is called perineural spread or perineural invasion.

Why Cancer Cells Can Spread

Cancer cells are physically different from normal cells. They are less "sticky," so they break away from the tumor more easily. They move through body tissues better. And they make proteins that break down the tissue around them, which helps them invade.

What Decides Where Cancer Spreads

The type of cancer and where it started matter most. Most cells that break free travel in the blood or lymph until they are caught in the next organ or set of lymph nodes "downstream." For example, breast cancer often spreads first to the lymph nodes under the arm (axillary lymph nodes), because they are closest to the breast. Many cancers spread to the lungs, because all the blood passes through the lungs.

The surroundings of the cancer — the tumor microenvironment — also matter. They depend on how much blood flow and how many nutrients there are, whether certain hormone receptors are present, and which immune cells are there, such as macrophages, neutrophils and natural killer (NK) cells. Some tissues suit certain cancers: prostate cancer often spreads to bone, because bone gives those cells conditions that help them live and grow. Some gene changes in cancer cells also make it easier for them to grow in certain organs.

Where Cancer Most Often Spreads

Besides lymph nodes, the most common places are the lungs, liver, bones and brain. Different cancers tend to go to different places:

• Bladder cancer — bones, liver or lungs
• Breast cancer — bones, brain, liver or lungs
• Colorectal, ovarian, stomach and pancreatic cancers — liver, lungs or the peritoneum (the lining of the belly)
• Kidney cancer — adrenal glands, bones, brain, liver or lungs
• Lung cancer — adrenal glands, bones, brain, liver or the other lung
• Melanoma — other areas of skin, muscle, bone, brain, liver or lungs
• Prostate cancer — adrenal glands, bones, liver or lungs
• Thyroid cancer — bone, liver or lungs
• Uterine (endometrial) cancer — bone, liver, lung, peritoneum or vagina

Questions to Ask Your Doctor

• Has my cancer spread to any lymph nodes or other parts of my body?
• Where is my type of cancer most likely to spread, and how will you check those places?
• Which tests will you use to look for spread, and how often?
• Does my cancer show perineural invasion, and what does that mean for me?
• Which symptoms could mean my cancer has spread, and should I report them right away?

Learn More

See Advanced and Metastatic Cancer for what it means when cancer has spread, and how that differs from a recurrence or a second cancer.

Source: https://www.cancer.org/cancer/understanding-cancer/what-is-cancer/how-does-cancer-spread.html