Screening for common cancers-how, whom and when to do it
Dr Ayekpam Anil Meetei
Non communicable diseases are now responsible for the majority of global deaths. According to estimate of World Health Organization, it is the second leading cause of death in the world. Cancer incidence and mortality are rapidly growing worldwide due to ageing and population growth, as well as changes in the prevalence and distribution of the main risk factors for cancer, including factors associated with socio-economic development. GLOBOCAN 2018 report estimates, there was an estimated 181 lakh new cancer diagnosed and 96 lakhs cancer death in the year 2018. 10 most common cancers worldwide in decreasing order are Lung, Breast, Colorectal, Prostrate, Stomach, Liver, Esophagus, Cervical, Thyroid and Urinary Bladder. Early diagnosis and treatment of cancers is one strategy to reduce the deaths due to cancer.
Cancer screening refers to performing a test or examination on an asymptomatic individual. Screening is an initial test which must be followed by more examination/tests to find out a disease in question. The goal of cancer screening is to prevent death and suffering from the disease in question through early therapeutic intervention. Screening must be distinguished from a diagnosis, where a patient complaint is investigated to find out the cause of the symptoms.
Four requirements must be met for screening a cancer.
i. The cancer burden is significant.
ii. The natural history of the disease is such that a detectable preclinical phase exists.
iii. A test or procedure must detect cancer earlier than if the cancers were detected as a result of the development of symptoms
iv. Treatment initiated earlier as a consequence of screening results is an improved outcome.
These requirements are necessary but not sufficient for the test or procedure to be efficacious. A screening test is effective when it leads to a decrease in cancer specific mortality. Common cancers which are amenable for screening include breast, colon, cervical and lung cancers. Some patients with a genetic mutation may need surveillance for a particular cancer, for example, surveillance for carcinoma ovary in a patient with BRCA mutation. The American Cancer Society (ACS) and US Prevention Services Task Force (USPSTF) are two organizations that issue widely used cancer screening guidelines, based on scientific evidences. The recommendations for screening of common cancers are enumerated below:
Breast Cancer : Clinical Breast Examination (CBE) is an annual physical examination of the breast by a trained medical staff. The Breast Self Examination (BSE) is a monthly self examination of her own breast. CBE and BSE may detect cancers during the interval between mammographic screenings and are useful as ancillary screening procedures. CBE and BSE alone are not recommended for screening breast cancer by ACS. Mammography is a low dose X-Ray of the breast and is the most effective screening method.
i) Yearly mammography starting at the age of 41.
ii) After age 55, patient may have a mammogram once in 2 years or continue to screen annually.
In our health set up, screening once in 2 years starting at age 50 years, as recommended by USPSTF is a more reasonable option.
Colon Cancer Screening : Colorectal cancer screening involves either stool testing for blood or DNA associated with polyps or cancer or structural examination looking for polyps or early cancer. Fecal Occult Blood test (FOBT) is a simple test to detect blood present in stool, which are shed from cancers in the colon. A positive FOBT needs to be investigated by colonoscopy. Colorectal cancer screening is recommended after age 45. The options for colorectal cancer screening are:
i) Annual FOBT
ii) Flexible Sigmoidoscopy every 5 years
iii) Colonoscopy every 10 years
iv) CT Colonography every 5 years
Colonoscopy and Sigmoidoscopy are invasive methods for screening. In our set up with limited health resources, annual FOBT is the only feasible option for mass screening.
Cervical Cancer Screening: Cervical cancer is the second most common cancer in Indian females. The most important cause of cervical cancer is infection by Human Papilloma Virus (HPV). Cervical cancer progresses through an ordered fashion with pre-invasive lesions developing before frankly invasive cancerous lesions. It is one of the cancers most suitable for screening.
PAP smear is a simple test to collect a sample of cell using a brush/spatula which is then examined for cancerous cells under a microscope. A HPV test uses a brush to collect cells and fluids from the cervix to examine for presence of human papilloma virus. Visual inspection after application of acetic acid in the cervix (VIA) is a cheap and convenient method but is less accurate and is used in resource limited setting.
i) Age 25 – 65 years-HPV testing every 5 years (or)
- Pap Smear every 3 years (or)
- HPV testing and PAP test every 5 years
ii) After age 65 years, screening may be discontinued with prior documented negative screening in the 10 years period before age 65.
A liquid based biopsy uses a brush to collect cells and fluids from the cervix, which are then used for HPV testing and cancerous cells, can be easily performed as an OPD procedure.
Lung Cancer Screening : Smoking is the most important cause of lung cancer. A person who smokes 20 cigarette sticks in a day for 1 year is quatified as 1 pack year and for 2 years as 2 pack years. A person who smokes 40 cigarette sticks in a day for 1 year is quantified as 2 pack years and for 2 years as 4 pack years. Lung cancer screening is recommended for individuals who are
i) Age 55 to 74 years
ii) At least 30 pack year smoking history
iii) Currently smoke or have quit with the past 15 years
Low dose CT (LDCT) uses only 1/5th of the conventional Chest CT radiation dose and usually takes only about 15 second to screen. LDCT is the preferred modality for Lung Cancer screening and Chest X-Rays are not recommended for Lung Cancer screening.
Screening for cancer should be a public health intervention. An opportunistic screening is where a patient sees a health care provider who chooses to screen or not to screen. Developed European countries have managed to reduce the mortality associated with these cancers by almost 20-30% with population screening. Screening is not without hazards. A screening test may miss cancers already present and give a wrong assurance. Fast growing cancers may develop during intervals of regular screening. It may also diagnose a non cancerous lesion as cancerous. Some cancers may also be detected which are not destined to metastasize or cause harm in the life span of the specific patient, a term medically called as overdiagnosis. Overdiagnosis may occur in the cancers of the thyroid, prostrate, kidney, neuroblastoma and melanoma. Screening for cancers is an evolving science and will continue to evolve with better evidences from well conducted trials. The above mentioned methods or procedures may be modified as per patient risk factors. Screening for common cancers and preventive measures as quitting smoking and vaccination will certainly have a impact on cancer mortality.
(The writer is a Consultant Surgical Oncologist at Shija Hospitals and is MS (Gen. Surgery), DNB (Surgical Oncology))