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Why Cancer can Recur

Posted: March 1, 2006

A cancer recurrence is the reappearance of disease that was thought to be cured or inactive (in remission). Cancer may recur after several weeks, several months, a few years, or many years.

Recurrent cancer starts from cancer cells that were not removed or destroyed by your original therapy. You may have had previous treatment that was meant to destroy the original cancer, as well as any cancer cells that may have moved to another part of your body.

Sometimes, no matter what treatment is used, a small number of cancer cells survive, and it may take a while for them to grow into tumors that are large enough to be detected.

A cancer recurrence is not the same thing as a new cancer, even if it appears in a new place in your body. A recurrence has the same type of cancer cells as the original tumor – no matter where it is found. For example, if you had colon cancer and it recurs in your liver, it is not liver cancer; colon cancer cells have spread to the liver, and the disease is still colon cancer. (The spread of cancer cells to a new part of the body is called metastasis.) This point is important because there are different treatments for different types of cancer.

Although it's possible to develop a second, entirely new tumor that is not related to your original cancer, this situation is more unusual than a recurrence.

Where cancer can recur
Not every cancer cell that breaks away from a tumor is able to grow elsewhere. Most are stopped by the body's natural defenses or destroyed by treatment. Cancers differ in their ability to recur and in the places where they are likely to show up.

Recurrent cancers are classified by location: local, regional, or distant.

• Local recurrence means that the cancer has come back in or very close to the same place as the original cancer. For instance, a woman who has had a mastectomy could later have a local recurrence of breast cancer in the area of her surgery. The term "local" also means that there is no sign of cancer in nearby lymph nodes or other tissues.
• A regional recurrence involves growth of a new tumor in lymph nodes or tissues near the original site but with no evidence of cancer at distant places in the body. A person who has had a melanoma removed from an arm, for instance, might have a regional recurrence in the lymph nodes under that arm.
• In distant recurrence, the original cancer has spread (metastasized) to organs or other tissues far from the site of origin. For example, a man who had prostate cancer could have a recurrence of that cancer in his bones. This man does not have bone cancer; he has prostate cancer that has spread to his bones.

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