- Cancers figure among the leading causes of morbidity and mortality worldwide, with approximately 14 million new cases and 8.2 million cancer related deaths in 2012 (1).
- The number of new cases is expected to rise by about 70% over the next two decades.
- Among men, the 5 most common sites of cancer diagnosed in 2012 were lung, prostate, colorectum, stomach, and liver cancer.
- Among women the 5 most common sites diagnosed were breast, colorectum, lung, cervix, and stomach cancer.
- About 30% of cancer deaths are due to the 5 leading behavioural and dietary risks: high body mass index, low fruit and vegetable intake, lack of physical activity, tobacco use, alcohol use.
- Tobacco use is the most important risk factor for cancer causing over 20% of global cancer deaths and about 70% of global lung cancer deaths.
- Cancer causing viral infections such as HBV/HCV and HPV are responsible for up to 20% of cancer deaths in low- and middle-income countries (2).
- More than 60% of world’s total new annual cases occur in Africa, Asia and Central and South America. These regions account for 70% of the world’s cancer deaths (1).
- It is expected that annual cancer cases will rise from 14 million in 2012 to 22 within the next 2 decades (1).
Cancer is a generic term for a large group of diseases that can affect any part of the body. Other terms used are malignant tumours and neoplasms. One defining feature of cancer is the rapid creation of abnormal cells that grow beyond their usual boundaries, and which can then invade adjoining parts of the body and spread to other organs, the latter process is referred to as metastasizing. Metastases are the major cause of death from cancer.
Cancer is a leading cause of death worldwide, accounting for 8.2 million deaths in 2012 (1). The most common causes of cancer death are cancers of:
- lung (1.59 million deaths)
- liver (745 000 deaths)
- stomach (723 000 deaths)
- colorectal (694 000 deaths)
- breast (521 000 deaths)
- oesophageal cancer (400 000 deaths) (1).
What causes cancer?
Cancer arises from one single cell. The transformation from a normal cell into a tumour cell is a multistage process, typically a progression from a pre-cancerous lesion to malignant tumours. These changes are the result of the interaction between a person's genetic factors and three categories of external agents, including:
- physical carcinogens, such as ultraviolet and ionizing radiation;
- chemical carcinogens, such as asbestos, components of tobacco smoke, aflatoxin (a food contaminant) and arsenic (a drinking water contaminant); and
- biological carcinogens, such as infections from certain viruses, bacteria or parasites.
WHO, through its cancer research agency, International Agency for Research on Cancer (IARC), maintains a classification of cancer causing agents.
Ageing is another fundamental factor for the development of cancer. The incidence of cancer rises dramatically with age, most likely due to a build up of risks for specific cancers that increase with age. The overall risk accumulation is combined with the tendency for cellular repair mechanisms to be less effective as a person grows older.
Risk factors for cancers
Tobacco use, alcohol use, unhealthy diet and physical inactivity are the main cancer risk factors worldwide. Some chronic infections are risk factors for cancer and have major relevance in low- and middle-income countries.
Hepatitis B (HBV), hepatitis C virus (HCV) and some types of Human Papilloma Virus (HPV) increase the risk for liver and cervical cancer respectively. Infection with HIV substantially increases the risk of cancer such as cervical cancer.
How can the burden of cancer be reduced?
Knowledge about the causes of cancer, and interventions to prevent and manage the disease is extensive. Cancer can be reduced and controlled by implementing evidence-based strategies for cancer prevention, early detection of cancer and management of patients with cancer. Many cancers have a high chance of cure if detected early and treated adequately.
Modifying and avoiding risk factors
More than 30% of cancer deaths could be prevented by modifying or avoiding key risk factors, including:
- tobacco use
- being overweight or obese
- unhealthy diet with low fruit and vegetable intake
- lack of physical activity
- alcohol use
- sexually transmitted HPV-infection
- infection by HBV
- ionizing and non-ionizing radiation
- urban air pollution
- indoor smoke from household use of solid fuels.
Tobacco use is the single most important risk factor for cancer causing about 20% of global cancer deaths and about 71% of global lung cancer deaths. In many low-income countries, up to 20% of cancer deaths are due to infection by HBV and HPV.
- Increase avoidance of the risk factors listed above.
- Vaccinate against human papilloma virus (HPV) and hepatitis B virus (HBV).
- Control occupational hazards.
- Reduce exposure to non-ionizing radiation by sunlight. (UV)
- Reduce exposure to ionizing radiation (occupational or medical diagnostic imaging).
Cancer mortality can be reduced if cases are detected and treated early. There are two components of early detection efforts:
The awareness of early signs and symptoms (for cancer types such as skin, cervical, breast, colorectal and oral) in order to get them diagnosed and treated at early stage. Early diagnosis is particularly relevant when there is no effective screening methods or – as in many low-resource settings– no screening and treatment interventions implemented. In absence of any early detection or screening and treatment intervention, patients are diagnosed at very late stages when curative treatment is not any more an option.
Screening is defined as the systematic application of a test in an asymptomatic in a target population. It aims to identify individuals with abnormalities suggestive of a specific cancer or pre-cancer and refer them promptly for treatment or when feasible for diagnosis and treatment. Screening programmes are especially effective for frequent cancer types for which cost-effective, affordable, acceptable and accessible screening tests are available to the majority of the population at risk.
Examples of screening methods are:
- visual inspection with acetic acid (VIA) for cervical cancer in low-resource settings;
- HPV testing for cervical cancer;
- PAP cytology test for cervical cancer in middle- and high-income settings;
- mammography screening for breast cancer in high-income settings.
A correct cancer diagnosis is essential for adequate and effective treatment because every cancer type requires a specific treatment regimen which encompasses one or more modalities such as surgery, and/or radiotherapy, and/or chemotherapy. The primary goal is to cure cancer or to considerably prolong life. Improving the patient's quality of life is also an important goal. It can be achieved by supportive or palliative care and psychological support.
Potential for cure among early detectable cancers
Some of the most common cancer types, such as breast cancer, cervical cancer, oral cancer and colorectal cancer have high cure rates when detected early and treated according to best practices.
Potential for cure of some other cancers
Some cancer types, even though disseminated, such as leukaemias and lymphomas in children, and testicular seminoma, have high cure rates if appropriate treatment is provided.
Palliative care is treatment to relieve, rather than cure, symptoms caused by cancer. Palliative care can help people live more comfortably; it is an urgent humanitarian need for people worldwide with cancer and other chronic fatal diseases. It is particularly needed in places with a high proportion of patients in advanced stages where there is little chance of cure.
Relief from physical, psychosocial and spiritual problems can be achieved in over 90% of advanced cancer patients through palliative care.
Palliative care strategies
Effective public health strategies, comprising of community- and home-based care are essential to provide pain relief and palliative care for patients and their families in low-resource settings.
Improved access to oral morphine is mandatory for the treatment of moderate to severe cancer pain, suffered by over 80% of cancer patients in terminal phase.
In 2013, WHO launched the Global Action Plan for the Prevention and Control of Noncommunicable Diseases 2013-2030 that aims to reduce by 25% premature mortality from cancer, cardiovascular diseases, diabetes and chronic respiratory diseases. Some of the voluntary targets are most relevant for cancer prevention such as the target about reducing tobacco consumption by 30% within the period 2014-2025.
WHO and the International Agency for Research on Cancer (IARC), collaborate with other United Nations organizations within the UN Noncommunicable Diseases Interagency taskforce (2014) and partners to:
- increase political commitment for cancer prevention and control;
- coordinate and conduct research on the causes of human cancer and the mechanisms of carcinogenesis;
- monitor the cancer burden (as part of the work of the Global Initiative on Cancer Registries GICR);
- develop scientific strategies for cancer prevention and control;
- generate new knowledge, and disseminate existing knowledge to facilitate the delivery of evidence-based approaches to cancer control;
- develop standards and tools to guide the planning and implementation of interventions for prevention, early detection, treatment and care;
- facilitate broad networks of cancer control partners and experts at global, regional and national levels;
- strengthen health systems at national and local levels to deliver cure and care for cancer patients; and
- provide technical assistance for rapid, effective transfer of best practice interventions to developing countries.
2. de Martel C, Ferlay J, Franceschi S, et al. Global burden of cancers attributable to infections in 2008: a review and synthetic analysis. The Lancet Oncology 2012;13: 607-615.