Metastasis occurs when breast cancer cells travel through the circulatory system and seed new cancer deposits called micrometastases. These tiny tumors are at first too small to detect, but in time the cells may keep on dividing in the new location. The tumors that the dividing cells form can only be detected by scans when they grow above a certain size, so a clear scan unfortunately doesnâ€™t mean that there is no cancer.
The terms used to talk about breast cancer can be confusing. When breast cancer spreads to another part of the bodyâ€”most commonly the bones, liver, lungs or brainâ€”it is referred to as metastatic breast cancer. When breast cancer has spread at the time it is first diagnosed, it is referred to as Stage IV breast cancer. Sometimes you will see the term â€śdistant metastasesâ€ť used, which refers to cancer that has spread beyond the breast and surrounding tissue. The term â€ślocal recurrence,â€ť refers to cancer coming back in the initial surgical area where a lumpectomy has been done. The term â€śregional metastasesâ€ť refers to the spread of disease to the chest wall and surrounding tissue, the skin around the scar, and to the lymph nodes under the arm, in the center of the chest and up around the collar bone. Regional metastases often carry a more favorable prognosis than distant metastasis, and may be treated differently.
Because the cancer cells that travel to metastatic sites still have characteristics of breast cancer and respond to breast cancer treatments, the disease is still called breast cancer even when it spreads to other parts of the body. So, itâ€™s not a brain cancer when breast cancer spreads to the brain; it is a brain metastasis from breast cancer.
Metastasis may occur in several locations at the same time, or in a single location. Metastatic breast cancer is most often thought of as a â€śsystemicâ€ť disease. This means that the cancer is presumed to have spread, at least microscopically, beyond the sites where metastases have been found. This has important implications for whether a localized treatment like surgery or radiation will be tried, or whether a drug that affects the whole body is used. While drugs are generally used that treat the whole body, there are a number of situations, for example brain and other CNS metastases, where localized treatments like radiation and surgery are used in conjunction with systemic treatments.
While the brain is usually not the first metastatic site, this sometimes happens, especially in women who have HER2-positive breast cancer, which spreads more frequently to the brain than cancer that is HER2-negative.
What are tumor markers?
Tumor marker tests, like CA 15.3 and CA 27.29, which measure proteins called antigens shed by tumors, and other experimental tests that count the numbers of cancer cells in the blood, can sometimesâ€”but not alwaysâ€”be early indicators of cancer progression. For many women with metastatic disease, tumor markers, in combination with scans, can be helpful indicators that a treatment is working, or beginning to fail. For others, periodic scans and how they are feeling, are much more reliable indicators.
Why wasnâ€™t my metastatic breast cancer found sooner?
Some women blame their doctors or themselves because their metastatic cancer wasnâ€™t found earlier, through follow-up testing and scans after their initial diagnosis of breast cancer. They worry that they might have been cured, had the spread of their cancer been found sooner. But research shows that when it comes to metastatic breast cancer, the concept of "early detectionâ€ť doesnâ€™t apply. Finding the cancerâ€™s spread before there are symptoms (with tumor marker tests and scans) and treating it a few months earlier offers no benefit in survival or quality of life. While metastatic breast cancer is often very responsive to treatment, and there are many treatments to be tried, in the overwhelming majority of cases, cure will no longer be possible. So, doctors treat metastatic breast cancer as a chronic disease that can hopefully be controlled for many years.