What is the meaning of cancer screening? Why do you need to know about these screening tests? Do these tests help in the early detection of cancer? How can these tests change the outcome of cancer? All these questions are important, and their answers can bring about remarkable changes in the prevention, early detection, and, ultimately, the outcome of cancer.

Introduction

Cancer screening means looking for cancer before the appearance of symptoms when cancer is easier to treat. Early diagnosis allows people to treat the disease effectively, leading to better outcomes.

Understanding early detection and prevention

Early detection of cancer focuses on detecting symptoms as early as possible so that people have the best chance for successful treatment. Symptomatic presentation is still the main way to diagnose most cancers; however, nowadays, many cancer screening tests have been developed to identify changes in the body or tissues that are suggestive of either the initial pathologies of cancer or early cancer. When abnormal tissue or cancer is found early, it may be easier to treat or cure. By the time symptoms appear, the cancer may have grown and spread.

Primary prevention

Screening tests are done to detect either a precancerous or cancerous condition from the start. For example, detection of colorectal polyps through screening techniques such as colonoscopy may suggest surgical removal of these polyps and prevent the development of cancer. This is termed as primary prevention. It simply means that timely screening to prevent the illness from happening.¹

Secondary prevention

If there is an early-stage tumour (e.g. detected through mammography or fecal blood testing, screening is termed secondary prevention because it is intended to improve long-term outcomes by treating cancer when it is more likely to be localized.² Therefore, secondary prevention stops the illnesses from getting worse and minimises the serious consequences of the disease.

What is the significance of early cancer detection?

Early cancer detection through screening tests has the following advantages:

• Identifying cancer at an early stage saves lives
• There are higher chances of better outcomes after treatment
• Early diagnosis and treatment prevent serious health conditions, disabilities, and death
• It is less costly to treat cancer when it is diagnosed early
• People can continue to work and support their families if they can access effective treatment in time

Statistics highlighting the success of early intervention in cancer cases

Almost 50% of cancers, when diagnosed, had already progressed to an advanced stage. Survival improves when cancer is detected early, as they allow early intervention. A review study highlights the contribution of cancer screening to decreasing the morbidity and mortality of cancer, with statistics of colorectal and breast cancer collected between 1990 and 2015 in the United States. The cancer mortality decreased by 25%, partially attributed to the introduction of cancer screening for colorectal and breast cancer.³

Features of screening tests

Screening aims to detect cancer at an early stage by inviting asymptomatic, apparently healthy people for testing. Ideally, cancer screening should be:⁴

• Minimally invasive or noninvasive
• Low cost
• Provide minimal false negatives or positive results
• Should minimize harm and maximize benefits of screening

How to know if you are at high risk of developing cancer?

You must have heard the term “high risk” about cancer. High-risk population refers to people who have an average chance of developing a certain kind of cancer. But how can you know if you are at risk of getting cancer or not? A high-risk population for common cancers refers to a group of individuals who have features that significantly raise their likelihood of developing a specific type of cancer. 

Family history of the disease 

If you have first-degree relatives (parents and siblings), and sometimes second-degree relatives (uncles, aunts, and first cousins) who have had cancer, it puts you in the high-risk population.

Genetic predispositions 

If you have a family history of multiple people with cancers or if you have had cancer at a younger age, then you may be genetically predisposed to certain types of cancer.

Lifestyle choices 

Lifestyle factors, such as alcohol consumption, smoking, diet, obesity physical inactivity, and reproductive and hormonal factors are considered as causes of cancer and main targets for primary prevention.⁵

Exposure to environmental carcinogens 

Up to 90% of cancer cases are caused by environmental factors or lifestyle. Tobacco smoke, air pollution, and haze account for > 85% of lung cancer deaths.⁶ Around 50% of stomach cancer might be triggered by environmental agents, mostly dietary habits. The World Cancer Research Fund (WCRF) summarized that fruit and vegetables are protectors against stomach cancer development, whereas broiled animal meats, salt-preserved foods, and smoked foods probably enhance stomach carcinoma progression.⁷

Identification of high-risk populations is important in the viewpoint of cancer prevention and early detection strategies. By identifying and focusing on the population at risk, healthcare professionals can implement more personalised and frequent screening protocols, leading to the timely identification of cancer when it is most treatable.⁸

Screening tests for common cancers   

Who is at risk of breast cancer 

Approximately half of breast cancers develop in people assigned female at birth (AFAB) who have no identifiable breast cancer risk factor other than gender and age, in the other half following are the risk factors.⁹

• People (AFAB) over 40 years of age 
• Obesity
• Excessive use of alcohol
• Family history of breast cancer
• History of radiation exposure,
• Reproductive history (e.g. age at that menstrual periods began and the age at first pregnancy)
• Tobacco use and postmenopausal hormone therapy⁹

Screening for breast cancer

Screening mammograms are the gold standard for breast cancer detection. It is the most widely used and most effective technique. It can detect a tumour before any symptoms or even before it is palpable.

The United States Preventive Services Task Force (USPSTF) endorses that people (AFAB), who are 50 to 74 years old and are at average risk for breast cancer should get a mammogram every two years. People who are 40 to 49 years old should talk to their doctor or other healthcare provider about when and how often to get a mammogram.

Other breast cancer screening methods:self-exams and clinical breast exams, ultrasound, and magnetic resonance imaging (MRI).¹⁰

Lung cancer

Lung cancer is the leading cause of death among cancer-related deaths. Smoking is the main causative factor responsible for this preventable ailment. Lung cancer is often diagnosed at an advanced stage however, screening of the population at risk can dramatically reduce mortality.¹¹

Who is at risk of developing lung cancer?

• Tobacco smokers (particularly cigarette smokers) are at most risk of developing lung cancer
• Workers in asbestos mines and industry
• Occupation exposure to chemicals like diesel engine exhaust, mustard gas, chromium compounds, etc
• Outdoor pollution
• Family history of lung cancer

Screening for lung cancer

The primary screening method for lung cancer is low-dose computed tomography (LDCT), in which you lie on a table and an X-ray machine uses a low dose of radiation to make thorough images of your lungs. USPSTF recommends annual screening for lung cancer with LDCT. Research has shown that, unlike chest X-rays, yearly LDCT scans to screen people at higher risk of lung cancer can detect the signs of cancer earlier.¹²

Prostate cancer

Prostate cancer is the second most commonly diagnosed cancer and the fifth leading cause of cancer death among people assigned male at birth (AMAB). Studies show that there has been a decline in incidence and mortality in the recent period, and this impact in decline is mostly attributed to prostate screening.¹³

Who is at risk of prostate cancer?

According to CDC, every 2 or 3 people AMAB in a hundred are at risk of getting prostate cancer. The older the person is, the higher the chance of getting this type of cancer. There may be a genetic predisposition if the family history is positive. If there are complaints of burning while passing urine or blood in semen or urine, one should get screened for prostate cancer.

Screening for prostate cancer

A blood test for detecting prostate cancer is called a prostate-specific antigen (PSA) detection test. PSA is a substance secreted by cells of the prostate gland. There can be higher levels of PSA in the blood of individuals with prostate cancer. However, there are controversies about the limitations of PSA screening since PSA may be elevated in other conditions of the prostate. Digital rectal examination is another alternative screening option for prostate cancer.¹⁴

Colorectal cancer

Colorectal cancer is the third most common cancer and mostly affects people above 50 years of age. It is often diagnosed at advanced stages when treatment options are limited. Several lifestyle factors, such as a high intake of processed meats and less intake of fruits and vegetables, a sedentary lifestyle, obesity, and excessive alcohol consumption, contribute to its development. 

Screening tests for colorectal cancers

The lifetime risk for developing colorectal cancer is 1 in 24 people. Studies show that some screening tests for colorectal cancer help find cancer at an early stage and may decrease the number of deaths from the disease.¹⁵

Colonoscopy is a pivotal screening method for colorectal cancers. Through this procedure, the doctor can look inside the rectum and colon for polyps, and if found, the polyps may be removed before they develop into cancer. 

Screening guidelines may change over time, and there is a crucial role of individual risk factors in determining the suitable screening strategy. It is important to remember to consult your doctor for your personalised health outcome depending upon your specific history and risk factors. 

FAQ

What tests are done to detect early cancer?

Common tests to detect early cancer include

• Mammograms for breast cancer
• Colonoscopies for colorectal cancer
• Pap smears for cervical cancer
• Prostate-Specific Antigen (PSA) tests for prostate cancer screening
• Regular skin examinations are important for detecting changes in moles or skin lesions that may indicate skin cancer
• Blood tests, imaging studies like CT scans, and genetic screenings may be employed based on individual risk factors and symptoms⁴

What are WHO guidelines for cancer screening?

• Cancer screening tests should be evidenced-based, balancing benefits and harms. The benefits of screening should outweigh potential harms, such as false positives or overdiagnosis
• Screening programs should be cost-effective and resource-efficient; based on sound scientific evidence and accurate; quality-assured for reliability and accuracy
• Individuals should be informed about screening tests' potential benefits and risks
• Effective treatment options should be available for the identified cancers
• Screening programs should target cancers with a significant health impact¹⁶

Can blood tests detect cancer in the body?

Certain blood tests can help detect cancer by identifying specific markers or abnormalities associated with the disease, such as tumour markers or irregular blood cell counts. However, definitive cancer diagnosis typically requires additional diagnostic procedures, such as imaging studies or tissue biopsies.¹⁷ 

What are important and common early warning signs of cancer?

Early signs of cancer are

• Unexplained weight loss
• Fatigue
• Night sweats
• Loss of appetite

Common cancer and their primary and secondary screening tests

Summary

Cancer screening means looking for cancer before the appearance of symptoms, when cancer is easier to treat. Early detection of cancer through these screening tests, give chance to people to have the best chance for successful treatment. These screening tests provide primary and secondary prevention against cancers like breast cancer, prostate cancer, cervical cancer, lung cancer, and a few more types of cancers. According to WHO guidelines, the benefits of screening should be greater than potential harms, such as false positives or overdiagnosis.