What Is Metastatic Cancer? Stage IV Explained

Metastasis happens when cancer cells break away from the original, or primary, tumour and travel through the bloodstream or lymphatic system to establish new tumours elsewhere in the body. These new tumours are made up of the same type of cancer cells as the original tumour, so a breast cancer that spreads to the bone is still called metastatic breast cancer, not bone cancer. Common sites of spread include the liver, lungs, bones, and brain, depending on the type of primary cancer.

A metastatic diagnosis often shifts the focus of care toward long-term management, similar in some ways to managing a chronic condition, with regular monitoring and adjustments to treatment over time. It can be helpful to discuss openly with your care team what realistic goals of treatment look like in your specific situation.

Symptoms of metastatic cancer depend on which organs are affected; for example, bone metastases may cause pain or fractures, liver metastases may cause abdominal discomfort or jaundice, lung metastases may cause cough or breathlessness, and brain metastases may cause headaches or neurological changes. Some metastases are found on scans before causing any symptoms.

Metastatic cancer may be diagnosed at the time of initial cancer diagnosis, called de novo metastatic disease, or it may be found later if a cancer that was previously treated returns and spreads, called recurrent or relapsed metastatic disease. Imaging studies are central to identifying the location and extent of spread.

In addition to imaging, blood tests and tumour marker levels may be monitored over time to help track how the cancer is responding to treatment. A biopsy of a metastatic lesion may also be performed to reassess molecular features relevant to treatment planning.

Almost any type of cancer can become metastatic, though patterns of spread vary; for example, breast and prostate cancers often spread to bone, while colorectal cancer frequently spreads to the liver. The behaviour of metastatic disease depends heavily on the original cancer type and its specific biology.

Treatment typically centres on systemic therapies, including chemotherapy, targeted therapy, hormone therapy, and immunotherapy, chosen based on the cancer type and its molecular features. Localised treatments such as radiation or surgery may be used alongside systemic therapy to manage specific symptomatic areas, and supportive and palliative care play an important role throughout treatment.