Cancer shows both geographic and temporal variability. There are different patterns of cancer at different places and different times. These patterns relate both to habits and to environmental hazards.
Habits: The use of tobacco has resulted in lung cancer in North America and Europe during the last half of the 20th century. Dietary habits underlie the high incidence of stomach cancer in Japan, Northern China, Chile and Eastern Europe. This tumor is associated with lower socioeconomic status. The incidence falls in second generation Japanese who have moved to the United States of America. Food preservation methods are associated with stomach and liver cancers in West Africa and Southeast Asia. Techniques for pickling as well as contamination with aflatoxins from mould are responsible. Environmental hazards:

Viruses: Hepatitis B Virus is associated with liver cancer.