Increase in Global Cancer Rates
The World Cancer Report

Introduction

Cancer rates could increase by 50% to 15 million new cases by 2020, according to the World Cancer Report.^1,2 The report also provides clear evidence that healthy lifestyles and public health action by governments and health practitioners could stem this trend, and prevent as many as one-third of cancers worldwide.

In 2000, malignant tumours were responsible for 12% of the nearly 56 million deaths from all causes worldwide. In many countries, more than one-quarter of deaths were attributable to cancer, with 5.3 million men and 4.7 million women developing a malignant tumour and 6.2 million people dying from the disease. Table 1 shows the most common cancers worldwide. The report also reveals that cancer has emerged as a major public health problem in developing countries, matching its effect in industrialised nations.

Table 1. Most common cancers worldwide.

The predicted sharp increase in new cases will mainly be due to steadily ageing populations in both developed and developing countries, but also to current trends in smoking prevalence and the increasing adoption of unhealthy lifestyles. From a global perspective, there is strong justification for focusing cancer prevention activities on the
2 main cancer-causing factors of tobacco and diet. Efforts to curb infections that cause cancer should also be increased. These factors were responsible for 2.7 million cancer deaths (43%) and 4 million new cases (40%) in 2000.

According to Dr Gro Harlem Brundtland, Director- General of the World Health Organization (WHO), the World Cancer Report provides a basis for public health action and assists in reducing the morbidity and mortality from cancer and improving the quality of life of cancer patients throughout the world. The following text is a summary of the World Cancer Report and its recommendations.

Tobacco - Primary Prevention

Tobacco consumption remains the most important avoidable cancer risk.² In the 20th century, approximately 100 million people died worldwide from tobacco-associated diseases (cancer, chronic lung disease, cardiovascular disease, and stroke). Half of regular smokers are killed by the habit and one-quarter will die prematurely during middle age.

The lung cancer risk for regular smokers as compared with non-smokers (relative risk, RR) is between 20- and 30-fold. In countries with a high prevalence of smoking and where many women have smoked cigarettes throughout adult life, approximately 90% of lung cancers in both men and women are attributable to cigarette smoking. The RR for bladder cancer is 5 to 6, and for cancers of the oral cavity, pharynx, larynx, and squamous cell carcinoma of the oesophagus, the RR is greater than 6, and 3 to 4 for carcinomas of the pancreas. These risk estimates are higher than previously thought and additional cancer sites with an RR of 2 to 3 have been identified as being associated with tobacco smoking, including cancers of the stomach, liver, uterine cervix, kidney (renal cell carcinoma), nasal cavities and sinuses, oesophagus (adenocarcinoma), and myeloid leukaemia.

Involuntary (passive) tobacco smoke is carcinogenic and may increase the lung cancer risk by 20%. There is currently no evidence that smoking causes breast, prostate, or endometrial cancer of the uterus. While it is best never to start smoking, epidemiological evidence supports the enormous benefits of smoking cessation. The greatest reduction in the number of cancer deaths within the next several decades will be due to those who stop the habit. The greatest effect results from stopping smoking during the early 30s, but an impressive risk reduction of more than 60% is obtained even when the habit is stopped after the age of 50 years. The report recommends a number of strategies to reduce global tobacco consumption, requiring the involvement of government and community health organisations, health care professionals, and individuals. The ground-breaking public health treaty the Framework Convention on Tobacco Control represents a powerful tool to ensure that such strategies are implemented. The Member States of the WHO have agreed to submit the treaty to the World Health Assembly in May 2003.

Infection and Cancer

In developing countries, up to 23% of malignancies are caused by infectious agents, including hepatitis B and C viruses (HBV, HCV), human papillomaviruses (HPV), and Helicobacter pylori (Table 2). In developed countries, cancers caused by chronic infections only amount to approximately 8% of all malignancies. This discrepancy is particularly evident for cervical cancer. In developed countries with an excellent public health infrastructure and a high compliance rate, early cytological detection of cervical cancer (Papanicolaou test) has led to an impressive reduction in mortality while, in other regions of the world, including Central America, Southeast Africa, and India, the incidence and mortality rates remain high, with more than 80% of all cervical cancer deaths occurring in developing countries.

Table 2. Malignancies caused by infectious agents.

Vaccinations could be key to preventing these cancers. Vaccination against HBV has already been shown to prevent liver cancer in high-incidence countries and it is likely that HPV vaccination will become a reality in a few years.

Poverty, Affluence, and Cancer

In developed countries, the probability of being diagnosed with cancer is more than twice that in developing countries. However, while approximately 50% of cancer patients die of the disease in wealthy countries, in developing countries, 80% of cancer patients have late-stage incurable tumours when they are diagnosed, pointing to the need for better detection programmes. The main reasons for the greater cancer burden of affluent societies are the earlier onset of the tobacco epidemic, earlier exposure to occupational carcinogens, and western nutrition and lifestyle. However, with increasing wealth and industrialisation, many countries are undergoing rapid changes that will greatly increase their future disease burden. Once considered a 'western' disease, cancer has now emerged as a major public health problem in developing countries.

Western Lifestyle and Risk

The western lifestyle is characterised by a highly caloric diet, rich in fat, refined carbohydrates, and animal protein, combined with low physical activity, resulting in an overall energy imbalance. Malignancies typical for affluent societies are cancers of the breast, colon/rectum, uterus, gallbladder, kidney, and adenocarcinoma of the oesophagus. Prostate cancer is also strongly related to the western lifestyle, but there is an additional ethnic component, in that black people appear to be at a greater risk than Caucasians and the latter at higher risk than Asian populations.

Stomach cancer is among the most common malignancies worldwide, with approximately 870,000 cases every year, and 650,000 deaths. Approximately 60% of cases occur in developing countries, with the highest incidence rates in East Asia, the Andean regions of South America, and Eastern Europe. However, stomach cancer is declining worldwide. In Switzerland and neighbouring European countries, the mortality rate fell by 60% within 1 generation. If this trend continues, stomach cancer may become a rare disease in some regions during the next 30 years.

The main reason for this development is the invention of the refrigerator, allowing fish and meat preservation without salting. In populations such as Japan and Korea that prefer salty food (salted pickles and salad) stomach cancer rates are still high but have also started to decline. An additional factor contributing to this trend is the availability of fresh fruit and vegetables throughout the year in many countries.

Cancer Prevention

Epidemiological studies indicate that the frequent consumption of fruit and vegetables may reduce the risk of developing cancers of epithelial origin, including carcinomas of the pharynx, larynx, lung, oesophagus, stomach, colon, and cervix. Recent data from the European Prospective into Cancer and Nutrition (EPIC) suggests that a daily consumption of 500 g of fruits and vegetables can decrease the incidence of cancers of the digestive tract by up to 25%. The report also states that, given the multi-faceted impact of diet on cancer, many countries should encourage consumption of locally produced vegetables, fruit, and agricultural products, and avoid the adoption of western dietary habits.

Early Detection

There is sound evidence that the recent decline in cancer mortality observed in many countries is largely due to early detection. Responsibility for this success lies with improvements in imaging (mammography, magnetic resonance imaging and computed tomography), and with the higher degree of disease awareness and educational programmes on typical early symptoms. Most successful so far has been the early detection of cervical cancer by cytology and of breast cancer by mammography. A recent analysis by an International Agency for Research on Cancer (IARC) Working Group concluded that, under trial conditions, mammography screening may reduce breast cancer mortality by 25% to 30% and that a reduction of 20% appears feasible for nationwide screening programmes. There is also emerging evidence that prostate cancer screening by assessment of serum prostate specific antigen levels may result in lower mortality rates, although management of early lesions remains invasive. For colon cancer detection, colonoscopy is considered the gold standard although its application in population-based screening programmes would require considerable medical resources.

Cancer Control Strategies

The aim of cancer control is a reduction in both the incidence of the disease and the associated morbidity and mortality, as well as improved quality of life for cancer patients and their families. The World Cancer Report emphasises the potential of early detection, treatment, and palliative care, and urges all countries to establish comprehensive national cancer control programmes, aimed at reducing the incidence of the disease and improving the quality of life for cancer patients and their families. In developing countries, in particular, where a large proportion of cancers are detected late in the course of the disease, efforts to achieve earlier diagnosis and delivery of adequate palliative care and pain relief require urgent attention.

In 2000 (the last year for which global data exists) approximately 400,000 women died from breast cancer, representing 1.6% of all female deaths. The proportion of breast cancer deaths was far higher in wealthy countries than in economically poor regions
(2% versus 0.5%). However, breast cancer mortality rates have started to decline in North America, Western Europe, and Australia, mainly due to improvements in early detection and treatment programmes such as chemotherapy and tamoxifen. Five-year survival rates are higher than 75% in most developed countries. The worldwide breast cancer epidemic has many causative factors, including reproductive history, genetics, radiation (especially at times of breast development), and the western lifestyle with its high caloric diet, obesity, and lack of physical activity.

The IARC recommends effective and carefully evaluated school education programmes for tobacco abstinence and healthy dietary habits. For a maximum impact, societies must change their priority from detection and treatment to prevention. At the core of the cancer control strategy are cost- effective interventions for the following components: tobacco control; infection control; healthy eating; a curable cancer programme; and palliative care. By acting now, countries can achieve significant reductions in cancer rates and in mortality from cancer by the year 2020.

References

1. Global cancer rates could increase by 50% to 15 million by 2020. World Health Organization Joint Press Release WHO/27/IARC/145. 3 April 2003.

2. The World Cancer Report the major findings. World Health Organization Joint Press Release WHO/27/IARC/145. 3 April 2003.