Metastasis

Cancer cells that metastasize have acquired abilities that normal cells do not have: they can detach from the original tumor, survive in the bloodstream or lymph fluid, invade a distant tissue, and establish a new tumor there. This is a complex, multi-step process, and most cancer cells that enter the bloodstream do not survive to form new tumors — but when they do, the resulting metastatic disease is the most serious form of cancer.

In breast cancer, metastasis most commonly occurs in the bones, lungs, liver, and brain. These sites are sometimes called "distant metastases" to distinguish them from cancer that has spread only to nearby lymph nodes. Metastatic breast cancer — also called stage IV breast cancer — is currently not curable, but it is treatable. Many women live for years with metastatic disease, managing it as a chronic condition with ongoing therapy.

Staging systems use the presence or absence of metastasis as a key variable. The "M" in the TNM staging system stands for metastasis: M0 means no distant spread has been found; M1 means it has. Imaging tests such as CT scans, PET scans, bone scans, and MRI are used to look for metastases when staging a new diagnosis or evaluating symptoms in a person previously treated for cancer.

Understanding metastasis helps you make sense of cancer staging and why your oncologist orders imaging tests at certain points in your care. It also clarifies what "early-stage" cancer means — catching cancer before it has spread gives treatment the best chance of eliminating it from the body completely.

If you have been diagnosed with metastatic breast cancer, knowing that treatment options have expanded considerably in recent years can provide real hope. Targeted therapies, hormone therapies, immunotherapy, and clinical trials have significantly extended the time many women live well with metastatic disease. Open, honest conversations with your oncology team about your goals and quality of life are at the center of this care.