What is Liver and what are It’s Functions?
Liver is the largest glandular organ in human body weighing about 1.4 kilograms in a healthy adult. It sits below the diaphragm and beneath the right ribs in the abdominal cavity. It is divided into two lobes by the falciform ligament, with right lobe being larger than the left one. Major functional cells of the liver are known as hepatocytes (specialized epithelial cells).
It receives blood from two main sources – oxygenated blood from the hepatic artery and deoxygenated blood containing absorbed nutrients (and other substances) from the hepatic portal vein. It performs many functions that include: secretion of bile (that help in digestion of fat); metabolism of carbohydrate, lipid, protein, and many drugs; excretion of bilirubin; storage of vitamins and minerals; phagocytosis; removal of worn out WBCs and RBCs; and activation of vitamin D.
Types of Liver Cancer
The overall incidence and mortality rate of liver cancer has been increasing during the last few decades, which is postulated to be due to the increasing incidence of hepatitis B and hepatitis C infections during this time. It is more common among men than women and mostly occur at an age of 55 to 64 years.
Hepatocellular carcinoma (HCC) (affecting hepatocytes) is the most commonly encountered (about 90% of the cases) liver cancer.
Intrahepatic cholangiocarcinoma (bile duct cancer) is also generally grouped with liver cancer, which affects cells lining the bile ducts (tubes that carry bile secreted by hepatocytes to the gallbladder and to the intestine) within the liver.
Angiosarcoma, hemangiosarcoma (affecting cells lining the blood vessels of the liver), and
Hepatoblastoma (that usually occur at younger age wherein cells resemble fetal liver cells) are some less common type of liver cancers. The liver is a vascular organ, and thus, is a common site of secondary cancers. However, in case of secondary cancers (cancers that originated somewhere else in the body and have spread to the liver), liver cancer is viewed as a part of primary cancer and treated in the way primary cancer is treated.
Risk Factors for Liver Cancer
Hepatitis B or C infection
Chronic infection with hepatitis B virus (HBV) or hepatitis C virus (HCV) is the well-recognized major risk factor for the liver cancer development. HBV is responsible for high incidences of liver cancer in Asia and Africa, while HCV is responsible for the high incidences of the disease in Europe, Japan, and North America.
Alcohol intake may act synergistically with these infections and can further increase the risk of developing liver cancer. Population at high risk of hepatitis induced liver cancer is males, family history of disease, age more than 45 years and patients with cirrhosis.
Hepatitis B has relative risk of 12.7,100 fold increased risk than non-carriers. Lifetime risk of liver cancer among HBV carriers in population where infection occurs early in life is 27% for males and 4% for females. Virus integrates into the hepatocyte genome causing microdeletions that can target cancer relevant genes.
Also, HBx can cause transcriptional activation altering the expression of growth-control genes. HCV is more likely to lead to chronic infections (10 % vs 60% to 80%) and cirrhosis ( 20-fold increase).
The average age of HBV-associated HCC is around 52 yr compared with 62 yrs for HCV is only about 30 yr ( compared with 40 to 50 yr for HBV ). HCV-associated HCC patients tend to have more frequent and advanced cirrhosis
Patients with liver cirrhosis remain at high risk of developing liver cancer. The cirrhosis may result from any of the following cause:
- excessive alcohol intake,
- chronic liver injury,
- inherited error of metabolism (for example, hemochromatosis – a condition characterized by increased absorption of iron due to mutation in HFE gene),
- Wilson’s disease,
- schistosomiasis (infection caused by a blood fluke), or
- alpha-1 anti-trypsin deficiency.
All these disorders have been reported to be the independent risk factor for liver cancer development.
Metabolic disorders and Obesity
Many studies have suggested that the presence of certain metabolic disorders like obesity, diabetes, impaired glucose metabolism, and non-alcoholic fatty liver is associated with increased risk of developing liver cancer.
Exposure to aflatoxin (produced by Aspergillus fungus that commonly contaminates peanuts, wheat, soybeans, groundnuts, corn, and rice), arsenic or microcystin in drinking water, vinyl chloride, and thorium dioxide have also been reported to increase the risk of liver cancer development.
Individuals with prolonged use of anabolic steroids are generally at higher risk of developing liver cancer.
Male gender and Ethnicity
Liver cancer is about 2 to 3 times more common in men compared to women, worldwide. This disparity is postulated to be related to the differential effect of androgen on the hepatocytes. According to different epidemiological studies, incidences of liver cancer are highest in Asians followed by African Americans and then Caucasians.
Chronic cigarette/tobacco smoking and prolonged use of oral contraceptives are less common risk factors for the development of liver cancer.
How can you Reduce the Risk?
Some of the risk factors of liver cancer are modifiable and other are non-modifiable. By making some lifestyle changes, liver cancer risk may be reduced.
- Regular exercise
- Weight control
- Eating a healthy diet
- Taking Alcohol in moderation
- Avoiding infection with Hepatitis B and C virus (avoid high risk sexual behaviour, vaccination)