The liver is a large organ situated in the upper right side of the abdomen, performing functions such as filtering toxins from the blood, producing bile, and processing nutrients. Metastasis is the process where cancer cells break away from their original tumor and travel through the bloodstream or lymphatic system to form a new tumor elsewhere. When cancer spreads to the liver, it is called metastatic liver cancer, a form of secondary cancer. The disease is named and treated according to its site of origin, not the liver itself.
Defining Metastatic Liver Cancer
Metastatic liver cancer is a tumor in the liver that originated elsewhere in the body. This is distinct from primary liver cancer, such as hepatocellular carcinoma (HCC), which begins in the liver cells themselves. Secondary liver cancer is much more common than the primary form in the United States and Europe.
A metastatic liver tumor is composed of cells genetically identical to the original primary tumor cells. For example, if breast cancer spreads to the liver, the tumor found there is made up of breast cancer cells. This cellular identity dictates that treatment approaches are based on the primary cancer type, not the liver itself. This distinction is important for effective management, as a drug designed to target colon cancer cells will be used even when those cells are residing in the liver.
Common Primary Cancer Sites
The liver is a frequent destination for cancer cells due to its function as the body’s largest filter and its unique blood supply. The most common source of cancer that metastasizes to the liver is colorectal cancer. Up to 70% of individuals with colorectal cancer may eventually develop liver metastases because the veins draining the large intestine flow directly into the liver via the portal venous system.
Cancers originating from other abdominal organs that empty into the portal vein, such as the stomach and pancreas, also commonly spread to the liver. Beyond the digestive tract, other cancers frequently metastasize to the liver, including those from the breast, lung, and kidney. The liver’s tendency to receive metastasis from a wide variety of malignancies is a direct consequence of its high volume of blood flow.
The Pathway of Spread
The journey of cancer cells from a primary tumor to the liver involves a multi-step process known as the invasion-metastasis cascade. It begins with cancer cells detaching from the original tumor and invading nearby tissue and blood vessel walls, a step called intravasation. Once inside the bloodstream, these circulating tumor cells must survive the environment as they travel to the liver.
The liver’s dual blood supply makes it susceptible to circulating cancer cells. Approximately 75% of the liver’s blood comes from the portal vein, which collects blood from the spleen, pancreas, and the entire gastrointestinal tract. This provides a direct route for tumor cells from colorectal or pancreatic cancers to be deposited into the liver’s specialized capillaries, called sinusoids.
Once cancer cells arrive in the liver, they must exit the bloodstream (extravasation) and begin to colonize the tissue. While microscopic metastases initially receive blood supply from the portal system, as tumors grow into detectable lesions, they progressively derive the majority of their blood from the hepatic artery. This shift, known as arterialization, is a hallmark of established liver metastases and is often exploited in liver-directed treatments.
Diagnosis and General Management Approaches
Diagnosis often begins with non-specific symptoms, including unexplained weight loss, fatigue, abdominal pain, or jaundice (yellowing of the skin and eyes) due to impaired liver function. Physicians use blood tests to measure liver enzyme levels, which can indicate if the organ is stressed. However, these symptoms are often subtle or absent in early stages, meaning the cancer is frequently detected during routine screening for the primary malignancy.
Imaging techniques confirm the presence and extent of tumors in the liver. A contrast-enhanced computed tomography (CT) scan is a common initial tool for surveying the abdomen and evaluating cancer spread. Magnetic resonance imaging (MRI) offers superior soft-tissue contrast, making it valuable for detecting small lesions and for surgical planning. Positron emission tomography (PET) scans enhance the detection of cancer cells, especially in distant areas, by highlighting metabolically active tissues.
Management of metastatic liver cancer is customized based on the primary cancer’s origin, the number and size of the liver tumors, and the patient’s general health. Systemic therapies, such as chemotherapy, targeted drug therapy, and immunotherapy, are the mainstay of treatment because metastatic disease is considered systemic. These treatments circulate throughout the body to control cancer cells wherever they reside.
For patients with a limited number of tumors, local and regional treatments may be combined with systemic therapy. Surgical resection, or removal of the cancerous part of the liver, is an option for certain patients, particularly those with colorectal liver metastases. Nonsurgical local treatments include ablation, which uses heat or cold to destroy small tumors, and radioembolization, which delivers microscopic radioactive beads directly to the tumor via the hepatic artery. The goal of treatment is to control tumor growth, manage symptoms, and achieve long-term survival in select cases.