When cancer cells break off the primary tumor and travel through the body to grow in a new location, it's called metastasis.
When cancer cells break off the primary tumor and travel through the bloodstream or lymphatic system and then grow in a new location, the process is called metastasis.
Metastatic cancer, for some but not all tumor types, is considered by many physicians and researchers to be an incurable disease, but many patients have a chronic course, living for a long time and leading functional, fulfilling lives.
Treatment and prognosis for metastatic cancers are dependent on the location or type of primary tumor, although sometimes the primary tumor cannot be located. When a cancer, such as breast cancer, spreads to another part of the body, such as the lungs, it is still considered breast cancer, not lung cancer, and is still treated with breast cancer drugs.
Most tumor cells don’t have the ability to metastasize, and those that do must evolve through several changes in order to establish a new tumor in a different location of the body. First, the cancer cells have to become self-propelled. Cells usually don’t move from the place they originate because they cannot move through the body’s barrier membranes. However, some tumor cells produce enzymes that eat away at the membranes, softening them enough for the cells to break through.
The direction of blood flow and the size of the cancer cells cause most to come to rest in the first capillary bed they encounter. Cells that invade lymphatic channels may be trapped in the first lymph node they enter, which is why the closest lymph nodes are examined to determine whether the cancer has spread. The cells may also escape to nearby nodes or grow in distant nodes, a process called skip metastasis.
Finally, cells must be able to grow in a distant site, and have to acquire additional changes to do so. The so-called microenvironment of metastases includes blood vessels, fibroblasts, and inflammatory cells, which are co-opted to assist in cancer’s survival and growth.
A number of resources are available to help patients learn more about metastatic cancer and to find support:
Metastatic Breast Cancer Network
National Hospice and Palliative Care Organization