Cancer
Cancer is a leading cause of death worldwide, accounting for nearly 10 million deaths in 2020, or nearly one in six deaths.
The most common cancers are breast, lung, colon, and rectum, and prostate cancers.
Around one-third of deaths from cancer are due to tobacco use, high body mass index, alcohol consumption, low fruit and vegetable intake, and lack of physical activity.
Cancer-causing infections, such as human papillomavirus (HPV) and hepatitis, are responsible for approximately 30% of cancer cases in low- and lower-middle-income countries.
Cancers can be cured if detected early and treated effectively.
Cancer is a generic term for a large group of diseases that can affect any part of the body. Other terms used are malignant tumors and neoplasms.
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 metastasis.
Widespread metastases are the primary cause of death from cancer.
The problem
Cancer arises from the transformation of normal cells into tumor cells in a multi-stage process that generally progresses from a pre-cancerous lesion to a malignant tumor.
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, alcohol, aflatoxin (a food contaminant), and arsenic (a drinking water contaminant)
biological carcinogens, such as infections from certain viruses, bacteria, or parasites
WHO, through its cancer research agency, the International Agency for Research on Cancer (IARC), maintains a classification of cancer-causing agents.
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
Tobacco use, alcohol consumption, unhealthy diet, physical inactivity and air pollution are risk factors for cancer and other noncommunicable diseases.
Some chronic infections are risk factors for cancer; this is a particular issue in low and middle-income countries.
Hepatitis B and C viruses and some types of HPV increase the risk for liver and cervical cancer, respectively.
Infection with HIV increases the risk of developing cervical cancer six-fold and substantially increases the risk of developing select other cancers such as Kaposi sarcoma.
Reducing the burden
Between 30 and 50% of cancers can currently be prevented by avoiding risk factors and implementing existing evidence-based prevention strategies.
The cancer burden can also be reduced through early detection of cancer and appropriate treatment and care of patients who develop cancer.
Many cancers have a high chance of cure if diagnosed early and treated appropriately.
Prevention
Cancer risk can be reduced by:
not using tobacco
maintaining a healthy body weight
eating a healthy diet, including fruit and vegetables
doing physical activity regularly, avoiding or reducing consumption of alcohol
getting vaccinated against HPV and hepatitis B if you belong to a group for which vaccination is recommended
avoiding ultraviolet radiation exposure (exposure to the sun and tanning devices) and/or using sun protection measures
ensuring safe and appropriate use of radiation in health care (for diagnostic and therapeutic purposes)
minimizing occupational exposure to ionizing radiation
reducing exposure to outdoor air pollution and indoor air pollution, including radon (a radioactive gas produced from the natural decay of uranium, which can accumulate in buildings — homes, schools, and workplaces)
Early detection
Cancer mortality is reduced when cases are detected and treated early. There are two components of early detection: early diagnosis and screening.
Early diagnosis
When identified early, cancer is more likely to respond to treatment and can result in a greater probability of survival with less morbidity, as well as 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 three components:
being aware of the symptoms of different forms of cancer and of the importance of seeking medical advice when abnormal findings are observed
access to clinical evaluation and diagnostic services
timely referral to treatment services
Early diagnosis of symptomatic cancers is relevant in all settings and the majority of cancers. Cancer programs should be designed to reduce delays in, and barriers to, diagnosis, treatment, and supportive care.
Screening
Screening aims to identify individuals with findings suggestive of a specific cancer or pre-cancer before they have developed symptoms.
When abnormalities are identified during screening, further tests to establish a definitive diagnosis should follow, as should referral for treatment if cancer is proven to be present.
Screening programs are effective for some but not all cancer types and in general are far more complex and resource-intensive than early diagnosis as they require special equipment and dedicated personnel.
Even when screening programs are established, early diagnosis programs are still necessary to identify those cancer cases occurring in people who do not meet the age or risk factor criteria for screening.
Patient selection for screening programs is based on age and risk factors to avoid excessive false positive studies. Examples of screening methods are:
HPV test (including HPV DNA and mRNA test), as preferred modality for cervical cancer screening and
mammography screening for breast cancer for women aged 50–69 residing in settings with strong or relatively strong health systems.
Quality assurance is required for both screening and early diagnosis programs.
Treatment
A correct cancer diagnosis is essential for appropriate and effective treatment because every cancer type requires a specific treatment regimen.
Treatment usually includes surgery, radiotherapy, and/or systemic therapy (chemotherapy, hormonal treatments, targeted biological therapies).
Proper selection of a treatment regimen takes into consideration both the cancer and the individual being treated. Completion of the treatment protocol in a defined period of time is important to achieve the predicted therapeutic result.
Determining the goals of treatment is an important first step.
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 support for the patient’s physical, psychosocial and spiritual well-being and palliative care in terminal stages of cancer.
Some of the most common cancer types, such as breast cancer, cervical cancer, oral cancer, and colorectal cancer, have high cure probabilities when detected early and treated according to best practices.
Some cancer types, such as testicular seminoma and different types of leukemia and lymphoma in children, also have high cure rates if appropriate treatment is provided, even when cancerous cells are present in other areas of the body.
There is, however, a significant variation in treatment availability between countries of different income levels and comprehensive treatment is reportedly available in more than 90% of high-income countries but less than 15% of low-income countries.
Palliative care
Palliative care is treatment to relieve, rather than cure, symptoms and suffering caused by cancer and to improve the quality of life of patients and their families.
Palliative care can help people live more comfortably. It is particularly needed in places with a high proportion of patients in advanced stages of cancer where there is little chance of cure.
Relief from physical, psychosocial, and spiritual problems through palliative care is possible for more than 90% of patients with advanced stages of cancer.
