Liver metastases are malignant (cancerous) tumors that originated at sites remote from the liver and spread to the liver via the bloodstream.

Common primary tumors that can spread to the liver include gastrointestinal cancers (colorectal cancer, pancreatic cancer, gastric cancer and esophageal cancer) breast cancer, lung cancer and melanoma. The reasons for such spread vary and depend both on blood flow and certain characteristics of different types of cancer cells. For example, cancers of the gastrointestinal tract often spread to the liver because blood flows directly from these organs to the liver. Cancer cells therefore have a direct path to the liver. Alternatively, melanoma usually spreads through the body's arteries to the liver.

The risk of cancer spreading to the liver depends on the primary cancer site. Liver metastases can be present at the time the primary cancer is diagnosed, or they can occur months or years after the primary tumor is removed.