Liver cancer happens when cells begin to multiply at a faster rate than they should and the unwanted cells form a growth. There are many types of liver tumours, only some of which are cancers. The most important classification is whether the tumours are benign (relatively harmless) or malignant (capable of spreading from the liver and thus more serious).
Hemangioma is the most common type of benign liver tumour. It is an abnormal growth of blood vessels of the liver that begins in the fetus. More than 10% of the normal population has hemanigomas in the liver. Most people with hemangiomas exhibit no symptoms and require no treatment. In rare cases, some hemangiomas may enlarge and bleed in which case they may need to be surgically removed.
Hepatic adenomas are benign tumours of liver cells. Most do not cause symptoms and do not require treatment. However, if they are large they may cause pain or blood loss in which case they may need to be removed. Hepatic adenomas occur more frequently in women and seem to be triggered in some cases by the birth control pill or by pregnancy.
Focal nodular hyperplasia (FNH) is a tumour-like growth of several cell types. Although FNH tumours are benign, it can be hard to distinguish them from liver cancers.
The most common form of primary liver cancer (cancer that starts in the liver) in adults is called hepatocellular carcinoma (HCC). It is a cancer of liver cells. This type of cancer can have different growth patterns. Some begin as a single tumour that grows larger. It may spread to other parts of the liver in later stages of the disease.
Liver cancer may also develop in more than one site in the liver and may grow into multiple tumours. This pattern is most often seen in people with liver cirrhosis.
Another liver cancer is called cholangiocarcinoma. It originates in the small bile ducts which are tubes that carry bile to the gall bladder.
Most cases of liver cancer are cancers that began somewhere else in the body and spread to the liver. This is called metastases. Because of its very high blood flow and many biological functions, the liver is one of the most common places for metastases to grow. Tumors that originally arise in the colon, pancreas, stomach, lung or breast can spread to the liver. These types of cancers are named after the place where they began (primary site) and are considered secondary liver cancers or cancer metastases. For example, cancer that started in the lung and spread to the liver is called metastatic lung cancer with spread to the liver. Secondary liver cancers are 30 times more prevalent than primary liver cancers.