The most recent collection of cancer incidence figures from around the world shows that the highest of all is in black African males in Bulawayo, Zimbabwe, while the next highest level is in the black population of the San Francisco Bay area of the USA. These men have a 19 per cent chance of developing cancer by the age of 61 if they don’t die of something else first. The lowest levels of cancer incidence occur among men in Nigeria, who have a 6 per cent chance of developing cancer by the same age. In women the highest cancer rate in the world is among the better off (i.e. white) groups in the US but women from less affluent areas (i.e. mostly racial minorities) still have quite high levels.
It is interesting to look at the different types of cancer prevalent in different areas, especially if they are occurring in the same country. While the total rates of cancer in black males in Zimbabwe and the USA and in females in North and South America are all similar, the organs in which they occur are quite different. Cancers of the liver and gullet are more often seen amongst black men in Zimbabwe where they are fifteen and three and a half time more common respectively than in the USA. Cancer of the cervix is five times more common in Colombian women than in women in the USA, and cancer of the breast is three times more common in the USA than in Colombia. In both sexes cancer of the colon and rectum occur between four and six times more frequently in the USA than in either Zimbabwe or Colombia.
Undoubtedly cancers were known in antiquity but evidence suggests that they were rare until this century and things have changed dramatically in the West in recent years. Three National Cancer Surveys in the US span thirty-two years and give a very accurate picture of what is happening to cancer incidence. The occurrence of cancer has gone up for some types and down for others but the overall trend is upwards. Colorectal (large bowel) cancer, and that of the prostate and bladder, and of course lung cancer, have all gone up whereas cancers of the mouth, pharynx, gullet, stomach, liver and biliary tract have all become less common. Over this period women have fared relatively well compared with men because they have not shared in the rise in lung cancer and have experienced a sharp drop in cancer of the cervix. Interestingly, in a country like Japan, cancer incidence figures were much like the Third World until 1930 but have now changed to a westernized pattern. The incidence of cancer of the stomach, gullet and liver is falling in Japan, and that of lung, pancreas, bowel and rectum is rising. Cancer of the breast is also on the increase in Japan.