Metastatic Cancer: Why Cancer Spreads

Why Does Cancer Spread?
Photo Credit: vitanovski / iStockPhoto.com
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Why Does Cancer Spread?

Cancer that is confined to a single organ or body system is scary. However, when we hear that cancer has metastasized, we know that the cancer has spread from that organ or body system into neighboring tissues. Often the quality of life and prognosis decreases once the cancer has metastasized.

Although we may have done everything right in terms of our treatment plan — chemotherapy, radiation, surgery, a combination of therapies — we are left wondering why and how our cancer spread.

Why Does Cancer Spread?

According to the American Cancer Society, where the cancer originates plays a role in where the cancer will metastasize.

When cancer metastasizes, it typically begins by spreading to a close lymph node or organ. It does this by cancer cells breaking free from the original tumor and being carried by lymphatic fluid or blood “downstream” until they get trapped. When the cancer cells get trapped, new tumors are formed.

For example, breast cancer cells that break away from breast tumor will often metastasize to the lymph nodes in the armpits. Many cancers will metastasize to the lungs; this is because the heart pumps blood throughout the blood vessels in the lungs before recirculating into the body.

It is also important to note that not all cancer cells that break free from a tumor will metastasize — often, the cells die before they can form a new tumor.

For the cancer cells to actually form a new tumor genetic changes must happen in the cells; at this time, doctors are just beginning to understand those genetic changes.

How Does Cancer Spread?

When we discuss the spread of cancer, “localized” means the cancer is still in the site of diagnosis. “Regional spread” means the cancer has spread, but it is still in surrounding tissues or lymph nodes. “Metastasis” means the cancer has spread to distant organs or lymph nodes.

  • Typically, when cancer spreads it is through hematogenous spread. Hematogenous spread is the method of metastasis discussed above, where cancer cells break away from the tumor and travel to a new location.
  • Cancer can also spread through invasion. This means that the tumor grows directly into surrounding tissues.
  • Cancer can spread anywhere in the body. However, it is most likely to spread to areas such as the brain, lungs, bones and liver.

Will All Cancer Eventually Become Metastatic?

No, not all cancer will spread. As previously mentioned, in order for cancer to spread to other areas in the body, genetic changes must occur.

This means any localized tumor has the potential to spread to other organs, but the proper genetic changes must occur at the right time for this to happen.

Keep in mind that when cancer cells are able to break free from the tumor, they must travel to their new location via blood or lymphatic tissue — and they have to survive the journey.

As previously mentioned, not all cells survive the journey; they survive if the body’s defense mechanisms are diminished.

It is also important to note that cancer may spread to other areas of the body but not cause any harm for years — they may actually lie dormant for a long time before the cells begin to proliferate again. This is called “tissue dormancy.”

There are a variety of possible reasons for tissue dormancy:

  • A lack of adequate blood supply may prevent the proper amount of oxygen and nutrients needed for growth of the tumor.
  • The environment may not be adequate for tumor growth.
  • Immune responses may prevent tumor growth.

More research is necessary is still needed to fully understand tumor dormancy.

The Future of Metastatic Cancer

While we obviously hope and pray for a cure for cancer, on the horizon doctors believe they may be able to detect which types of cancers are prone to metastasis. They would do so by looking at genetic changes in the cancer cells.

Research is also being done on treatments that focus on blocking the genetic changes that cause cancer cells to metastasize.

Resources

American Cancer Society (What is Metastatic Cancer?)

Canadian Cancer Society (How Cancer Spreads)

Dana-Farber Cancer Institute (How Does Cancer Spread?)

Metastasis Research Society (Understanding Metastasis – For Patients)