Metastatic cancer is cancer that has spread from the part of the body where it started (its primary site or origin) to other parts of the body. When cells break away from a cancerous tumor, they can travel to other areas of the body through the bloodstream or lymphatic system. Several factors play into whether or not cancer will metastasize, including the site and staging of the original cancer. These factors can be indicative of the sites to which the cancer may spread, i.e.: breast cancer can metastasize to the bone, brain, liver, and lungs. It is more common for cancers to spread through the blood than the lymphatic system. The following is what is involved in the spread of cancer cells beyond the primary site.

  • The cells break away from the original tumor and enter the bloodstream or lymphatic system, which can carry them to another part of the body.
  • The cells attach to the wall of a blood or lymph vessel and move through it into a new organ.
  • The cells find a way to grow and thrive in their new location.
  • The cells avoid attacks from the body’s immune system.

In some cases, metastatic tumors have already started to grow when the primary cancer is first detected and diagnosed. In other cases, a metastasis may be found before the original (primary) tumor is diagnosed. If cancer has already spread to other places when it is detected, it is more difficult to determine its original origin, which makes it challenging to treat. In these patients, the cancer is referred to as cancer of unknown primary. Mortality from cancer is caused in large part by metastases, rather than the primary cancer. Many cancers have a propensity to spread to specific areas of the body, which can help oncologists and cancer specialists determine potential metastatic patterns and survival rates.

Metastatic Cancer Patterns and Statistics

  • Although cancer rarely begins in the liver, it is often one of the first places where cancer spreads. The liver is a primary organ with a very rich blood supply along with a unique microstructure, allowing cancer cells to easily enter and take hold there. An estimated 80 percent of cancers in the liver begin as primary tumors in other sites of the body, i.e., in the colon.
  • The August 2015 news that former President Jimmy Carter has cancer in the brain tied to primary melanoma may seem very surprising. Following a complete physical evaluation, his physicians detected cancer in his liver. After the surgery, which removed one-tenth of his liver, a biopsy confirmed that the cancer was melanoma, but more tests are needed to determine the site of the primary melanoma. Melanoma can spread anywhere in the body, with the liver and brain being two of the most common sites. Although melanoma spreads to the brain more commonly in males than in females, gender does not play a role in the overall incidence of secondary brain tumors.
  • Research has shown that women with breast cancer appear to be at higher risk of developing a meningioma, a benign type of primary brain tumor, than those who have not had breast cancer.

The following is a list of areas of the body that are most often affected by metastases, and the primary cancers that metastasize to each site.

Adrenal Gland: Kidney, Lung, Prostate

Bone: Bladder, Breast, Kidney, Lung, Melanoma (skin cancer), Prostate, Thyroid, Uterine

Brain: Breast, Colorectal, Lung, Kidney, Melanoma (skin cancer)

Liver: Bladder, Breast, Colorectal, Esophagus, Lung, Kidney, Melanoma (skin cancer), Ovarian, Pancreatic, Prostate, Stomach, Thyroid, Uterine

Lung: Bladder, Bone, Breast, Bowel, Colorectal, Kidney, Melanoma (skin cancer), Ovarian, Pancreatic, Prostate, Soft Tissue Sarcoma, Stomach, Testicular, Thyroid, Uterine

Patients with cancer including breast and colorectal are often given radiation or chemotherapy after surgery in an attempt to kill cancer cells that might have broken away from the primary tumor. This can lower the risk that the cancer will recur and spread. Groundbreaking research and more sophisticated testing methods have led to improved prognoses in patients with cancers that have metastasized. One such test is Cancer TYPE ID, a proprietary molecular test that aids in the determination of tumor type and subtype in metastatic cancer patients with an unclear diagnosis.