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 a major cause of death from cancer.
Cancer is a leading cause of death worldwide, accounting for 8.8 million deaths in 2015. The most common causes of cancer death are cancers of:
- Lung (1.69 million deaths)
- Liver (788,000 deaths)
- Colorectal (774,000 deaths)
- Gastric (754,000 deaths)
- Breast (571,000 deaths)
What causes cancer?
Cancer arises from the transformation of normal cells into tumour cells in a multistage process that generally progresses from a pre-cancerous lesion to a malignant tumour. These changes are the result of the interaction between a person’s genetic factors and 3 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).
- Biological carcinogens, such as infections from certain viruses, bacteria, or parasites.
The World Health Organization (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 major cancer risk factors worldwide and are also the 4 shared risk factors for other noncommunicable diseases.
Some chronic infections are risk factors for cancer and have major relevance in low- and middle-income countries. Approximately 15% of cancers diagnosed in 2012 were attributed to carcinogenic infections, including Helicobacter pylori, Human papillomavirus (HPV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), and Epstein-Barr virus (EBV).
Hepatitis B and C virus and some types of HPV increase the risk for liver and Cervical Cancer, respectively. Infection with Human Immunodeficiency Virus (HIV) substantially increases the risk of cancers such as Cervical Cancer.
Reducing the cancer burden
Between 30–50% of cancers can currently be prevented. This can be accomplished by avoiding risk factors and implementing existing evidence-based prevention strategies. The cancer burden can also be reduced through early detection of cancer and management of patients who develop cancer. Many cancers have a high chance of cure if diagnosed early and treated adequately.
Modify and avoid risk factors
Modifying or avoiding key risk factors can significantly reduce the burden of cancer. These risk factors include:
- Tobacco use including cigarettes and smokeless tobacco.
- Being overweight or obese.
- Unhealthy diet with low fruit and vegetable intake.
- Lack of physical activity.
- Alcohol use.
- Sexually transmitted HPV-infection.
- Infection by hepatitis or other carcinogenic infections.
- Ionizing and ultraviolet radiation.
- Urban air pollution.
- Indoor smoke from household use of solid fuels.
- Tobacco use is the single most important risk factor for cancer and is responsible for approximately 22% of cancer-related deaths globally.
Pursue prevention strategies
To prevent cancer, people may:
- Increase avoidance of the risk factors listed above.
- Vaccinate against HPV and hepatitis B virus.
- Control occupational hazards.
- Reduce exposure to ultraviolet radiation.
- Reduce exposure to ionizing radiation (occupational or medical diagnostic imaging).
- Vaccination against these HPV and hepatitis B viruses could prevent 1 million cancer cases each year.
Cancer mortality can be reduced if cases are detected and treated early. There are 2 components of early detection:
When identified early, cancer is more likely to respond to effective treatment and can result in a greater probability of surviving, less morbidity, and less expensive treatment. Significant improvements can be made in the lives of cancer patients by detecting cancer early and avoiding delays in care.
Early diagnosis consists of 3 steps that must be integrated and provided in a timely manner:
- Awareness and accessing care.
- Clinical evaluation, diagnosis and staging.
- Access to treatment.
Early diagnosis is relevant in all settings and the majority of cancers. In absence of early diagnosis, patients are diagnosed at late stages when curative treatment may no longer be an option. Programmes can be designed to reduce delays in, and barriers to, care, allowing patients to access treatment in a timely manner.
Screening aims to identify individuals with abnormalities suggestive of a specific cancer or pre-cancer who have not developed any symptoms and refer them promptly for diagnosis and treatment.
Screening programmes can be effective for select cancer types when appropriate tests are used, implemented effectively, linked to other steps in the screening process and when quality is assured. In general, a screening programme is a far more complex public health intervention compared to early diagnosis.
Examples of screening methods are:
- Visual inspection with acetic acid (VIA) for Cervical Cancer in low-income settings.
- Human Papillomavirus (HPV) testing for Cervical Cancer.
- Papanicolaou (PAP) cytology test for Cervical Cancer in middle- and high-income settings.
- Mammography screening for Breast Cancer in settings with strong or relatively strong health systems.
A correct cancer diagnosis is essential for adequate and effective treatment because every cancer type requires a specific treatment regimen that encompasses one or more modalities such as surgery, radiotherapy, and chemotherapy. Determining the goals of treatment and palliative care is an important first step, and health services should be integrated and people-centred. The primary goal is generally to cure cancer or to considerably prolong life. Improving the patient’s quality of life is also an important goal. This can be achieved by supportive or palliative care and psychosocial support.
Potential for cure among early detectable cancers
Potential for cure of some other cancers
Some cancer types, even when cancerous cells have traveled to other areas of the body, such as Testicular Seminoma and Leukaemias and Lymphomas in children, can have high cure rates if appropriate treatment is provided.