CANCER IN POPULOUS COUNTRIES
In the most populous country in the world, with over 1,300 million people spread over a vast area, the difficulty in obtaining cancer figures is even greater than for elsewhere. Notwithstanding data collection problems, it is clear that by the 1990s cancer had become the second most common cause of death in China, as in so many other countries. In 2008 the major cancers were of the lung, stomach, liver and bowel for both sexes, together with oesophageal cancer for men and breast cancer for women. The rates are rising, there is, for example, 130,000 more deaths from breast cancer in 2005 than there were in 2000 and this is the trend for leukaemia and cancers of lung, liver, bowel and prostate in men, and for breast, lung, liver, bowel and cervical cancer in women. At the same time the incidence of some cancers is declining – notably stomach, oesophagus and nasopharynx – as is mortality from cervical cancer. These improvements are due to the dramatic changes occurring in China as sanitary conditions and diets improve and screening programmes are introduced. The latter are extensive for employees of the government and major companies who provide annual health checks that may be beginning to have an impact on mortality rates for some cancers. On the other hand, as in the Western world, these changes are increasing lifespan and, together with the continuing widespread use of tobacco, the overall result is that cancer rates in China are rising by about 3% each year. Currently, lung cancer kills over 1,200 Chinese every day and the WHO estimates that by 2025 there will be a million new cases a year. By then annual tobacco deaths in China will exceed three million.
With a population (1,140 million) only slightly smaller than that of China, India is also undergoing a transition to being a ‘developed’ nation. This means that there is migration from country to city, a general change in lifestyle and a rising life expectancy. Overall cancer rates are lower than in more developed countries (by about three times compared with the USA, for example) despite the rates for oral and oesophageal cancers being among the highest in the world (chewing betel is generally held to be responsible). The most common Indian cancers in men are lung, oesophageal, stomach and larynx; for women they are cervical, breast, ovarian and oesophageal and the total cancer death figure is currently about 600,000 per year. Unfortunately, the taking place means that, like many other developing nations, the numbers of people dying from non-communicable diseases such as cancer and heart disease are growing.
We have noted the prediction of 16 million new cancer cases in 2020, 70% being in the developing world. Sub-Saharan Africa will contribute over 1 million of these but, as might be predicted, the patterns across the different regions of Africa show wide variation (Fig. 1).
The major forms are liver and prostate in men and breast and cervical cancer in women, although AIDS has propelled the otherwise rare Kaposi sarcoma to the top of the table in some countries (Uganda, Swaziland, Malawi and Zimbabwe). Seventy per cent of cervical-cancers arises from infection by human papillomavirus (HPV). Liver cancer, major cancer in males, is caused by hepatitis viruses, mainly hepatitis B virus (HBV), which is carried by about 12% of the population. More than 2 billion people, mostly in Africa and Asia, are infected with HBV, accounting for a good deal of the 600,000 deaths a year from liver cancer.
Although there are no effective vaccines against both HPV and HBV, these have not yet been used on a significant scale in Africa, where the expenditure on health per head of the population is minute compared with developed nations, with the result that when cancers are detected they have usually advanced beyond the treatable stage. As yet there is no hepatitis C virus (HCV) vaccine, and existing therapies are limited, often poorly tolerated and frequently ineffective.
The global data raise the general question of why the incidence of different cancers is so variable. We’ve noted several factors (tobacco, diet, economics, etc.), to which we will return later, but yet another is the infection. Cervical and liver cancers dominate the global picture but are less prominent in the developed countries because most cases occur as a result of infection by viruses.
One of the most interesting questions arising from all the global cancer data is: how are things changing? Most countries in the developed world have produced a gradual decline in their total cancer mortality rate (Fig. 2).
Nevertheless, Japan has maintained its position of having one of the lowest rates and the UK remains significantly worse than the USA. from cardiovascular disease and was also high in the cancer league – mainly due to the factors we’ll come back to (heavy tobacco use, high-fat diet and low vegetable consumption). The effect of a national effort to improve these aspects of lifestyle has been to reduce heart disease in men by at least 65% and to reduce cancer mortality to one of the lowest rates in the world, thereby extending the average life expectancy of its citizens by over six years.