Metastatic cancer is cancer that has spread from its site of origin to another part of the body. The original cancer is called the primary tumor, and the cancer in another part of the body is called metastatic cancer. Metastatic cancer has the same type of cancer cells as the primary cancer. For example, breast cancer that spreads to the lung is called metastatic breast cancer, not lung cancer. It is treated as stage IV breast cancer, not as lung cancer. Metastatic cancer is also called metastatic tumor, tumors, or disease, metastasis (one cancerous tumor), metastases (more than one cancerous tumor), or advanced cancer.

Metastasis occurs when cancer cells break away from the primary tumor and enter the bloodstream or lymphatic system, allowing them to travel to other parts of the body and form new tumors. The most common places for distant metastases are the bones, brain, liver, and lungs. Metastatic cancer can cause a variety of symptoms, depending on the location of the new tumors. Some common symptoms include pain, cough, shortness of breath, unexplained weight loss, severe fatigue, or night sweats.

There are treatments available for most types of metastatic cancer, and the goal of treatment is often to control the cancer by stopping or slowing its growth. Some people can live for years with metastatic cancer that is well controlled, and other treatments may improve the quality of life by relieving symptoms. This type of care is called palliative care and can be given at any point during cancer treatment. Researchers are studying new ways to kill or stop the growth of primary and metastatic cancer cells, including helping the immune system fight cancer and disrupting the cancer cells ability to communicate with each other.