Liver metastases, or secondary liver cancer, occur when cancer cells from a tumor in another part of the body travel through the bloodstream or lymphatic system and establish new tumors in the liver. The liver is a frequent destination for metastatic disease because it receives a large volume of blood from two sources: the hepatic artery and the portal vein. This abundant dual blood supply, combined with the liver’s function as a filter, makes it a common site for circulating cancer cells to become trapped and grow.
Understanding Secondary Liver Cancer
Secondary liver cancer is fundamentally different from primary liver cancer, which begins in the liver cells themselves. When cancer spreads to the liver, the metastatic tumors are composed of the same type of cells as the original primary tumor, not liver cells. For instance, a cancer that began in the colon and spread to the liver is still treated as metastatic colorectal cancer, not liver cancer. This distinction dictates the choice of treatment, as the cancer cells respond to therapies specific to their origin.
The spread of cancer cells often follows the path of blood flow from the original tumor site. Cancers originating in the gastrointestinal tract, such as the colon, stomach, and pancreas, frequently metastasize to the liver via the portal vein. The portal vein collects nutrient-rich blood from the intestines and directs it straight to the liver for processing, providing a direct route for circulating tumor cells. Approximately half of all patients diagnosed with colorectal cancer will develop liver metastases at some point.
Colorectal cancer is the most common primary tumor to spread to the liver. Other common primary cancers that frequently spread to the liver include lung, breast, and neuroendocrine tumors. For these non-gastrointestinal cancers, tumor cells typically travel through the systemic circulation supplied by the hepatic artery. The environment of the liver is particularly hospitable for the colonization and proliferation of these foreign cancer cells.
Identifying Symptoms and Diagnostic Tools
Liver metastases often cause no symptoms in their early stages, as the liver has a large functional reserve and can continue to operate normally even with small tumors. When symptoms do appear, they are often vague, including general fatigue, unexplained weight loss, and loss of appetite. As the disease progresses, patients may experience pain or a feeling of fullness in the upper right side of the abdomen.
More pronounced symptoms can arise if the metastases obstruct the flow of bile or significantly impair liver function. Jaundice, the yellowing of the skin and the whites of the eyes, occurs due to the buildup of bilirubin. Other physical signs include dark-colored urine, pale stools, and ascites, which is the accumulation of fluid causing swelling in the abdomen. Physicians use blood tests to measure liver function, checking for elevated levels of enzymes like alanine aminotransferase (ALT) and aspartate aminotransferase (AST), or high bilirubin levels, which can indicate liver cell damage or obstruction.
Diagnosis relies heavily on imaging modalities to detect the tumors and determine the extent of the spread.
Imaging Techniques
Contrast-enhanced computed tomography (CT) scans are often used as an initial survey to check for both hepatic and extra-hepatic involvement. Magnetic resonance imaging (MRI) provides more detailed, high-resolution images of the soft tissues and is considered more sensitive than CT for detecting small liver lesions. Positron Emission Tomography (PET) scans, often combined with CT (PET/CT), use a radioactive tracer to highlight metabolically active cancer cells throughout the body. PET/CT is valuable for comprehensive staging, as it can detect tumors that have spread outside the liver.
A definitive diagnosis requires a biopsy, where a small sample of the liver tumor tissue is removed. This tissue is examined under a microscope to confirm the presence of cancer cells and identify their origin, which is crucial for guiding treatment. Biopsies are typically guided by ultrasound or CT imaging to ensure accurate and safe sampling of the lesion. The biopsy also allows for molecular and genetic testing of the tumor cells, which can help select the most effective systemic therapies.
Major Treatment Approaches
The management of liver metastases is highly individualized, determined by the type of primary cancer, the number and location of the tumors, and the patient’s overall health. Treatment plans are developed by a multidisciplinary team of specialists to combine systemic, local, and surgical options. Systemic therapies treat the entire body and are the foundation of care for most metastatic cancers.
Systemic Therapies
This category includes traditional chemotherapy, which uses drugs to kill rapidly dividing cells. More modern systemic treatments involve targeted therapies and immunotherapy. Targeted therapies focus on specific molecular pathways that drive cancer growth and are often used when the tumor has a known genetic mutation. Immunotherapy works by harnessing the patient’s own immune system to recognize and destroy cancer cells. These advanced approaches are frequently used to convert initially inoperable liver metastases into resectable ones.
Local Therapies
Local therapies are interventions that target the tumors directly within the liver while sparing surrounding healthy tissue. Ablation techniques, such as radiofrequency ablation (RFA) and microwave ablation (MWA), use heat energy delivered through a needle to destroy small tumors. These procedures are minimally invasive and can be an alternative for small, deep-seated tumors.
Another class of local treatments is embolization, which involves injecting substances directly into the blood vessels feeding the liver tumors. Transarterial Chemoembolization (TACE) involves delivering a high dose of chemotherapy combined with tiny particles to block the tumor’s blood supply. A specialized type of embolization is Y-90 radioembolization, which uses microscopic beads containing the radioactive isotope yttrium-90. These microspheres deliver a high, localized dose of radiation with minimal effect on the rest of the liver.
Surgical resection, which involves removing the portion of the liver containing the metastases, offers the best potential for a cure in select patients. This option is most commonly and successfully applied to liver metastases that originated from colorectal cancer. For patients with resectable colorectal liver metastases, five-year survival rates can exceed 50% following surgery. Surgery is only feasible if the tumors can be completely removed while leaving behind a sufficient volume of healthy liver tissue to ensure adequate post-operative function.