A screening test is a procedure that is performed to detect the presence of a specific disease. The individual or group of individuals (as in mass screenings) does not present any symptoms of the disease.
The purpose of a cancer screening test is to identify the presence of a specific cancer in an individual that does not demonstrate any symptoms. Screening allows for early detection of cancer and can save the life of the person who might have died if the cancer was not detected by screening. If cancers are detected early, the treatment can be more effective and often less costly than if the cancer had progressed and needed drastic treatment.
Most screening tests have been developed to be noninvasive or mildly invasive. For example breast self-exams, mammograms, and pelvic exams may be uncomfortable but are non-invasive. Therefore, most screening tests will not be affected by medications that a patient may be taking or other unrelated conditions a patient may be experiencing.
Before developing or administering a screening test, the effectiveness of the test needs to be evaluated. There are several criteria to consider when deciding whether or not to screen. First, is the cancer highly fatal and common? If yes, then it is suitable for screening. Second, in order to screen a cancer, there must be detectable pre-symptomatic indicators. Finally, the reliability of results needs to be evaluated. A test can have one of the four following outcomes: true positive, false positive, true negative, and false negative. Randomized controlled trials also help to identify effective screening.
Screening tests exist for many of the more common cancers such as prostate cancer , breast cancer , colon cancer , lung cancer, and cervical cancer . Each screening test has an advisable age to begin screening and a recommended frequency at which the test should be performed. As people age, cancer becomes more prevalent; therefore, more screening tests are recommended.
Prostate cancer screening
Prostate cancer affects many men each year. Screening includes a digital rectal exam, tests for prostate-specific antigen (PSA), and transrectal ultrasonography (TRUS). Each of these tests takes less than half an hour to perform. The PSA test is an excellent tool as it is highly sensitive, reasonably priced, and well-tolerated by patients. Men should be counseled about the benefits and risks of detecting and treating an indolent tumor (this cancer may not have caused symptoms). The treatment may cause urinary and sexual problems.
Breast cancer screening
After skin cancer, breast cancer is the most common malignancy that is diagnosed in women. There are several screening methods that can be performed, including breast self-exam (performed by the patient), clinical breast exam, mammography , and BRCA-1 and BRCA-2 genetic testing . Genetic testing is offered to patients that have a familial history of breast cancer. All of these tests can be performed in the doctor's office and take less than half an hour. Genetic testing requires a blood sample, and it takes a few days to receive the results. Counseling is strongly advised prior to genetic testing.
Colon cancer (colorectal cancer) is the third leading cause of cancer death in the United States and is the third most diagnosed cancer among both men and women. Screening tests include fecal occult blood test , flexible sigmoidoscopy , barium enema , and colonoscopy . High-risk patients (significant familial history) should begin screening at puberty or 10 years prior to occurrence of family member's tumor. Sigmoidoscopy and colonoscopy are slightly invasive, completed under mild sedative in the hospital on an outpatient basis, and take about 15 and 30 minutes respectively. Screening with colonoscopy is unique and reliable, because it allows visualization of the entire colon.
Most screening procedures are non-invasive in order to make them convenient for patients and cost effective. Screening such as breast exams, mammography, pelvic exams, digital rectal exams, and tests that require blood samples require no preparation by the patient. However, barium enema, sigmoidoscopy, and colonoscopy all require prior preparation of the bowel. Patients will be asked to consume a clear liquid diet 24 hours prior to the exams, followed by liquid laxative about 2 hours prior to the exam. An enema or two may be required until the stool is clear.
Since most of the exams are non-invasive, there is no required aftercare. However, patients are encouraged to monitor themselves for any related symptoms of the cancer in question.
Since no medical tests are perfect, there are several negative consequences associated with screening. First, if a patient's prognosis would be the same with or without the screening, then the patient experiences a longer time of being sick. Second, if the results of the tests are a false negative, then the patient may be negligent in identifying symptoms and warning signals. Conversely if the results of the test are a false positive, then the patient may be subjected to unnecessary diagnostic procedures and psychological trauma. Finally, insurance companies or employers that possess results of a positive genetic test, could use that information unethically, impacting coverage and employment advances.
Normal results vary for each test and need to be analyzed for false negative results.
Doctors schedule more diagnostic testing if abnormal results arise. Normally, a biopsy is administered on the tissue in question in order to view the cells for typical cancer traits.
See Also Pap smear; Tumor grading; Tumor staging
Bast, Robert C. Cancer Medicine. Hamilton, Ontario: B.C. Decker Inc., 2000.
Cook, Allan R. The New Cancer Sourcebook. Detroit: Omni-graphics, Inc., 1996.
DeVita, Vincent T., Jr. Cancer Principles and Practice of Oncology. 5th ed. Vol. 1 and 2. Philadelphia: Lippincott-Raven Publishers, 1997.
Ruffin, Mack T., M.D., et al. "Predictors of Screening for Breast, Cervical, Colorectal, and Prostatic Cancer Among Community-Based Primary Care Practices." The Journal of the American Board of Family Practice (January/Febru ary 2000): 1-10.
Brogdon, Cynthia F., R.N., M.S.N., AOCN, ACRN. "Women and Cancer." Journal of Nursing (November/December 1998): 344-55.
Sally C. McFarlane-Parrott
BRCA-1 and BRCA-2
—These are tumor suppressor genes whose inherited mutations have been associated with hereditary forms of breast cancer.
Digital rectal exam
—The physician will feel the prostate for irregular symmetry by going into the rectum.
—This tests for the presence of specific genes or the presence of mutations on specific genes.
Prostate-specific antigen test
—This test measures the level of prostate antigen in the blood to identify presence of prostate cancer.
—This test uses a small rectal probe to create an image of the prostate gland.
QUESTIONS TO ASK THE DOCTOR
- What medications interfere with the results of this test?
- What tests can be performed to confirm that the results of this screening test are accurate?
- What is the most accurate and cost-effective screening test for the type of cancer in question?
- Can this test be performed anonymously?
- Will my insurance company pay for this test?