Geographical Causes

Geography plays a role in the development of cancer. It has been observed that the incidence of oesophageal cancer is particularly high in the geographical band covering South-East Africa, Iran, Afghanistan, Central Asia, Mongolia and North China. The incidence of pancreatic cancer is higher in the Western countries and lower in Japan. On the other hand, stomach cancer is more common in Japan as compared to the Western countries. Similarly, the incidence of breast cancer varies appreciably in different parts of the world, being higher in the USA and lower in the Orient. Studies from Norway, Canada, USA and Australia have shown that the incidence of malignant melanoma increases considerably as one approaches the equator, probably due to the greater exposure to ultraviolet radiation.