From a moral and ethical perspective, prevention of a disease is pre¬ferable to the treatment of a disease. A critical ingredient of any prevention program therefore should focus on identifying people with a disease, and those at risk of developing a disease. With symptoms of a disease, people can seek medical attention.
But what if symptoms are not apparent?
Inexpensive screening tests allow medical practitioners to separate individuals at risk of disease or with disease, from the general popula¬tion. Having identified these individuals, they can then be subjected to the more expensive diagnostic tests to obtain a full diagnosis. An effective screening test has both a high sensitivity and specificity. Sensitivity refers to the ratio of diseased individuals that are test-positive and specificity to the ratio that are test-negative. The test should also be cost-effective, simple, non-invasive or minimally invasive, and easy to administer so it can enjoy high acceptance.
Currently, there is no lung cancer screening test. Chest x-ray and sputum cytology are used to diagnose lung cancer. Unfortunately, by the time these tests detect tumors the cancer is often too advanced to treat or has spread to other organs. While Spiral Computed Tomography (CT) and Positron Emission Tomography are effective at detecting lung cancer, they are either too resource intensive or costly to fulfill the role of screening tests. They are therefore more suitable for diagnosing lung cancer.
For breast cancer screening, the American Cancer Society recom-mends that women perform regular breast self-examinations. For women over 40, the Society recommends an annual mammogram, and an annual clinical breast examination. For women in their 20s and 30s, the Society recommends a clinical breast examination every three years. A good screening test tries to find the disease before there are symptoms. Mammography, the currently accepted form of screening, is very resource intensive and is not sensitive enough to detect very early-stage of breast cancer. A mammogram is an uncomfortable x-ray of the breast. The breast is placed on a flat surface while applying pressure via a compression device. This is necessary as it enables the doctor to see the breast in its entirety.
There are inherent limitations as a screening tool and its accuracy is affected by the skill of the technologist who takes the image, the proficiency of the radiologist who interprets it, and how well the X- ray equipment has been calibrated. Mammograms are not perfect and normal breast tissue can hide a malignancy, which is known as a false negative: cancer is present but it is not shown on the mammogram. A mammogram can pick up an abnormality that may look like cancer but may turn out to be nothing, which is called a false positive. False positives can lead to unnecessary biopsies and other invasive interven¬tions. In addition, it can lead to an emotional rollercoaster for both patients and their families.
The American Cancer Society also recommends that individuals should start screening for colorectal cancer at age 50. They suggest an annual fecal occult blood test, flexible sigmoidoscopy every five years, double contrast barium enema every five years, and a colonoscopy every 10 years.
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