Epidemiology, risk factors, and natural history of hepatocellular carcinoma

The incidence of hepatocellular carcinoma is increasing in many countries. The estimated number of new cases annually is over 500,000, and the yearly incidence comprises between 2.5 and 7% of patients with liver cirrhosis. The incidence varies between different geographic areas, being higher in developing areas; males are predominantly affected, with a 2:3 male/female ratio. The heterogeneous geographic distribution reflects the epidemiologic impact of the main etiologic factors and environmental risk, which are the hepatitis B (HBV) and hepatitis C (HCV) viruses. The percentage of cases of hepatocellular carcinoma attributable to HBV worldwide is 52.3% and is higher in Asia where the seroprevalence of HBsAg in the population is high. However, the vaccination campaign against this virus in some eastern countries has tended to lower the incidence of new cases of hepatocellular carcinoma. The percentage of cases of hepatocellular carcinoma attributable to HCV is 25%, and it is more prevalent in Japan, Spain, and Italy where the association between hepatocellular carcinoma and antibodies to HCV ranges between 50 and 70%. In most cases hepatocellular carcinoma develops in cirrhotic livers, where the persistent proliferation of liver cells represents the key factor of progression to hepatocellular carcinoma independent of the etiology. Another minor risk factor is aflatoxin B1 consumption, which is responsible for most cases of hepatocellular carcinoma in Africa, where the consumption of contaminated foods is common. Other known risk factors are some hereditary diseases, such as hemochromatosis, porphyria cutanea tarda, hereditary tyrosinemia, and alpha1 anti-trypsin deficiency. The natural history of hepatocellular carcinoma is heterogeneous and is influenced by nodule dimension, the mono- or plurifocality of lesions at diagnosis, the growth rate of the tumor, and the stage of the underlying cirrhosis. Available data to date suggest that tumor growth in a cirrhotic liver is variable and that the time in which a lesion in undetectable until it becomes 2 cm is between 4 and 12 months. Therefore, the suggested interval for surveillance screening with ultrasound in patients with liver cirrhosis has been set at 6 months. Patients who should benefit from screening programs are those who would be treated with curative therapy if diagnosed with hepatocellular carcinoma. Thus, the ideal target population should be limited to Child-Pugh's class A cirrhotic patients without significant comorbidity.