Cancer screening
The objective of cancer screening is to detect cancer before symptoms appear, involving various methods such as blood tests, urine tests, DNA tests, and medical imaging. The purpose of screening is early cancer detection, to make the cancer easier to treat and extending life expectancy. In 2019, cancer was the second leading cause of death globally; more recent data is pending due to the COVID-19 pandemic.
Universal screening, also known as mass screening or population screening, involves the screening of individuals within certain age and gender groups, aiming to screen the population for particular cancers or cancer risk factors. Selective screening, also known as targeted screening, identifies individuals with a higher risk of developing cancer, including individuals with a family history of cancer or individuals engaging in high-risk behaviors such as smoking.
The act of cancer screening plays a pivotal role in both preventing cancer and providing early diagnosis, contributing to increased success rates in treatment and ultimately extending life expectancy. Controversy arises when it is not clear whether the benefits of the screening outweigh the risks associated with the screening procedure, as well as the subsequent diagnostic tests and cancer treatments. Cancer screening is susceptible to producing both false negative and false positive results, underlining the importance of considering the possible errors in the screening process. Additionally, cancer screening can lead to overtreatment if the screening identifies a tumor that is ultimately benign.
Medical uses
Early detection of cancer is the main advantage of cancer screening, it gives the patient a better chance of surviving or even preventing the cancer. Screening can also help relieve the public burden cancer has on society both financially and socially. The EU's Beating Cancer Plan wishes to make sure that 90% of the population with sufficient risk is screened for breast, cervical and colorectal cancer; around 1.3 million people die from cancer in the EU each year.Risks
Several factors are considered to determine whether the benefits outweigh the associated risks and costs of cancer screening. Cancer screening trials have demonstrated only a minimal decline in cancer related deaths, and the evaluation of risks to benefits remains an important in determining the overall effectiveness of the cancer screening program.- While many screening tests are non-invasive, it is important to note that mammography involves ionizing radiation exposure. The breast is highly radiation sensitive, and it receives an approximate dose of 2.6 milligrays per mammography screening. There is however no evidence or research indicating that mammography screening itself directly causes cancer. Additionally, procedures like colonoscopy conducted with sedation, carry a potential risk of perforation.
- Overdiagnosis occurs when cancers or tumors are detected that would never pose harm to an individual. Breast cancer, prostate cancer, and colorectal cancer are examples of cancer types that are prone to overdiagnosis. The consequences of overdiagnosis and overtreatment resulting from cancer screening can lead to a decline in quality of life, due to the adverse effects of unnecessary medication and hospitalization.
- The accuracy of a cancer screening test relies on its sensitivity, and low sensitivity screening tests can overlook cancers. Additionally, a test lacking specificity can incorrectly indicate cancer in a healthy individual. All cancer screening tests generate both false-positive and false-negative results, with a tendency to yield more false positives.
- False-negative tests may provide a false sense of reassurance, possibly leading to a bad prognosis if the cancer is diagnosed at a later stage, despite the utilization of surgeries, therapies, and other treatments.
- The impact of early cancer detection and the treatment outcomes vary, as there are instances where even with available treatment, early detection may not enhance the overall survival. If the cancer screening does not change the treatment outcome, the screening only prolongs the time the individual lived with the knowledge of their cancer diagnosis. This phenomenon is called lead-time bias. A useful screening program reduces the number of years of potential life lost and disability-adjusted life years lost. However, recent studies suggest that in many cases, early detection of cancer increases the likelihood of survival.
- The extent to which a cancer is treatable depends on various factors, including the individual's life expectancy or if the individual is in the end stages of an existing chronic condition. In these cases, ignoring a cancer diagnosis can contribute to a better quality of life. If the cancer diagnosis would not lead to a change in care, cancer screening would not result in a positive outcome for the individual. Overdiagnosis in this case occurs, for example, in patients with end-stage renal disease and a study recommend against cancer screening for such patients.
- For older patients, discussing whether screening is appropriate based on their life expectancy can be uncomfortable for both doctor and patient. Avoiding these conversations can lead to inappropriate screening. Some studies showed that cancer center websites tended to omit information about age cutoffs, along with other information about the downsides of unnecessary screenings.
Attendance
A 2019 study indicated that individuals with mental health disorders are nearly 25% less likely to attend cancer screening appointments. Among them, women with schizophrenia have the lowest screening rates. Even those with common mood disorders, such as anxiety and depression, are less likely to attend compared the general population. The lower attendance rates are believed to contribute to the earlier mortality of people with mental health disorders.
In 2019, a study indicated that women with mental health disorders in Northern Ireland were less likely to participate in screening for breast cancer in comparison to women without mental health disorders. The documented attendance rate persisted even after accounting for variables, such as marital status and social deprivation.
A study published in 2020 reported that individuals from minority ethnic communities are also less likely to participate cancer screening initiatives. The study showed that British-Pakistani women encountered cultural and language barriers and were not aware that breast cancer screening do not take place in a female-only environment. In the UK, women of South Asian heritage display the lowest likelihood of participating in breast cancer screening. Further studies is still necessary to identify the specific barriers for the different South Asian communities.
Deprivation has been recognised as an additional factor contributing to the decrease of individuals attending cancer screening. A UK study indicated that making cancer screening easily accessible increased attendance. Providing mobile screening units parked in supermarket car parks, for example in the poorer areas of Manchester, was a viable approach for offering lung checks to high-risk groups. A simple test measured obstruction to the airflow in and out of the lungs. A third of the tests revealed airflow obstruction, indicating chronic obstructive pulmonary disease, a risk factor for lung cancer and various other health conditions.
By type
Breast cancer
Breast cancer is the most common cancer for women. Screening is done to detect the disease early in asymptomatic women, in an attempt to achieve an earlier diagnosis and lower mortality. Different screening tests are used for breast cancer screening, including clinical and self-examination of the breasts, mammography, and magnetic resonance imaging. Mammography is the standard method for breast cancer screening. This method is reported to give a 40% reduction in the risk of dying from the disease. Breasts with less fat and more fibrous tissue are known as dense breasts, they are a risk factor for breast cancer. The tissue makes it harder to find tumors while doing a mammogram, therefore MRI screening is proposed to supplement the mammogram in these patients.Like other cancers there are advantages and disadvantages to screening for breast cancer, with risks of harm by overdiagnosis, a possibility of radiation-induced cancer and false positives. From organized programmes it is estimated that 20% of women with 10 screens from ages 50 to 70 will get a false positive result, less than 5% of these cases will result in further invasive treatment. Radiation-induced cancer from screening with mammography has been approximated to be around 1 to 10 per 100,000 women, which is lower than the estimate of death from breast cancer itself.
Mutations of the genes BRCA1 and BRCA2 can increase the risk of breast cancer in the patients lifetime. In the US, risk factors for breast cancer like the BRCA gene and age are taken into consideration to decide if a screening test is needed and if so which is best for the person.
Many European countries have organized population-level screening programmes for breast cancer. In 2022, the European Commission's Scientific Advice Mechanism concluded that women should be screened for breast cancer earlier, starting while in their mid 40s.
Cervical cancer
Cervical cancer is the fourth most common cancer for women with an estimated 340,000 deaths according to the World Health Organization. HPV disease is the leading cause of cervical cancer, therefore making the HPV vaccine the primary prevention measure for the cancer. Screening with the Papanicolaou test is consequently the second measure of prevention. The test identifies cells that are precancerous, and are often credited for the reduced mortality.WHO encourage implementing population-based screening programs. There is a considerable range in the recommended age at which to begin screening around the world. The US does not follow a nation-wide program, and guideline recommendations differ, with some states recommend commencing screening at age 21 and others at 25; the intervals for testing also very, with intervals ranging from 3–5 years. The EU has guidelines for its member states when it comes to cancer screening, but they are not obliged to follow them as they are merely for assistance; it recommends population-based screening programs from age 30 using HPV tests with 5 year intervals.
In 2022, the European Commission's Scientific Advice Mechanism concluded that improved cervical cancer screening, combined with widespread HPV vaccination, presented an opportunity to eliminate cervical cancer in Europe.