The global cancer burden & cancer prevention strategies

1. Introduction

Cancer is the second most common cause of death globally, accounting for an estimated 9.6 million deaths in 2018. Over the coming decades, it is projected that low and middle-income countries will be hit the hardest by the continued increase in cases and deaths. Many of those cases can be prevented, or at the very least treated effectively when there is an early diagnosis.

This IARC World Cancer Report 2020 presents the most comprehensive, up-to-date science on cancer prevention, including statistics, causes, and mechanisms, and how this can be used to implement effective, strategies for cancer prevention and early detection. Priority was given to recent epidemiological findings that have contributed to an increased understanding of etiology or, in some rare cases, prevention. In this context, WHO unveils cancer control measures that could save 7 million lives.

2. How is cancer burden distributed over the world?

Cancer has surpassed cardiovascular diseases but mortality rates from cancer are declining in most higher-income countries while this is not the case in lower-income countries. There are marked differences between countries or regions in cancer mortality, with an increasing burden in low- and middle-income countries, attributable both to less-than-optimal implementation of preventive measures and to diagnosis at a later stage of cancer development.

Cancer remains the first or second leading cause of premature death (i.e. at ages 30–69 years) in 134 of 183 countries. It ranks third or fourth in an additional 45 countries. Of the 15.2 million premature deaths from non-communicable diseases worldwide in 2016, 30 % were due to cancer.

The different patterns of causes of death such as behavioural factors (e.g. tobacco use, harmful alcohol consumption), unhealthy diet, physical inactivity, metabolic factors (e.g. high blood pressure, overweight and obesity, and high cholesterol level), and environmental factors should help to prioritize approaches to reduce mortality in a given country.

3. What are the global trends in cancer incidence and mortality?

For several tumour types – colorectal, prostate, lung and breast cancer – high incidence rates were once restricted to North America, western Europe, and Australia while low income countries primarily had a relatively high incidence of stomach, liver, and cervical cancer. Now, changes in incidence over time for these and other cancer types illustrate an evolution and variations between countries. The predicted global cancer burden by 2040 is expected to exceed 27 million new cancer cases per year, a 50% increase on the estimated 18.1 million cancers in 2018, with the greatest increase in countries with low or medium Human Development Index (HDI).

For specific cancers:

• For lung cancer, tobacco smoking is responsible for 63% of overall global deaths from and for more than 90% of lung cancer deaths in countries where smoking is prevalent in both sexes; further, lung cancer survival remains low globally;
• Rising breast cancer incidence rates are correlated with trends towards earlier ages at first menstruation, later ages at first birth, and lower number of births. In countries with high income, incidence rates have stabilized after a marked decline in incidence starting in about 2000, which is considered to result from the reduction in menopausal hormone replacement therapy as well as earlier detection and effective screening programmes;
• Colorectal cancer incidence rates of have increased in countries in transition and in younger age groups and in recent generations in a diverse set of countries; declining incidence trends are observed predominantly in older age groups (55 years and older) of some HDI countries subject to early detection. Some preventive therapies such as regular use of low dose aspirin, is thought to have contributed as well.;
• For prostate cancer, the evolution of observed incidence rates (an increase followed by a decline) is attributed to the clinical testing of a prostate specific antigen (PSA);
• Stomach cancer, which ranks 5^th in terms of incidence and 3^th in terms of mortality, is decreasing (predominantly of the type attributable to infection with Helicobacter pylori), whereas incidence of cancer strongly associated with overweight and obesity is increasing in several populations;
• Cervical cancer incidence and mortality rates have declined in most countries in recent decades as a result of the detection of precancerous lesions by screening. Global elimination of the disease is attainable during this century through Human Papilloma Virus (HPV) vaccination and screening programmes, even if increasing rates have been observed in younger generations of women in some countries.
• Chronic infections are responsible of about 13% of cancers worldwide, or 2.2 million cases per year. Helicobacter pylori, human papillomaviruses, hepatitis B virus, and hepatitis C virus contribute most to the burden of cancer caused by infections globally.

4. Are children particularly sensitive to cancer?

Cancer is indeed a major cause of death in children and the incidence of childhood cancers is increasing worldwide in both high- and low-income regions. Cancer types in children are different from those in adults; the most common cancer types being leukaemia, lymphoma, and tumours of the central nervous system.

Compared with adults, children are more vulnerable to environmental agents, because of their unique activity patterns, behaviour, and physiology, as well as the immaturity of their organs. In addition, many children – especially those living in low-income regions of the world – are involved in hazardous work, such as that involving contact with pesticides, and are exposed to emerging threats such as toxic components of electronic waste (e-waste).

5. What are the main basis for cancer prevention strategies?

Feasible, affordable, and cost-effective interventions that reduce exposure to the key causes and other risk factors for cancer, increased access to essential health-care services and vaccines are crucial for cancer disease control globally. In addition, individual behaviour change should lower personal risk of multiple noncommunicable diseases, including cancer.

Cancer incidence can be reduced by decreasing or eliminating exposure to carcinogens in multiple contexts. Evidence from comprehensive community programmes suggests that a combination of behavioural strategies, commitment, and national and local action are key factors in the design of programmes and policies of cancer prevention.

Tobacco control and vaccination policies are two of the most notable successes in cancer prevention. Success in reducing the incidence of smoking-related cancers in some countries indicates a range of measures that may be researched for their efficacy in other situations. Interventions to change behaviour related to nutrition, exercise, and weight gain are being actively researched.

 

 

Vaccination is effective for some cancers caused by infectious agents, notably the hepatitis B and HPV vaccines. Other infections such as those by Helicobacter pylori and hepatitis C are curable.

An increased risk of cancer may also be indicated by family history and can be addressed by monitoring the affected individuals. For women at high risk of breast cancer, reductions of 30–70% in the incidence of breast cancer can be achieved with use of anti-estrogenic agents such as tamoxifen.

Also, the report underlines that the widespread use of low-dose aspirin for 10 years between ages 50 years and 65 years could have the largest potential impact on the population at large on cancer incidence and mortality.

Early detection of cancer is another critical component of cancer control. In addition to reduction of mortality from a specific cancer type, a proper approach to cancer screening should ensure that the harms do not outweigh the benefits.

 

 

In addition to the characteristics of the intervention, the capacity of the public health infrastructure and the health delivery system to implement and sustain a prevention strategy is fundamental. Universal access to health care is important for the delivery of the preventive intervention and also for cancer care and outcomes of care.