Essentially, no cancer produces signs or symptoms at the outset. During this period, which varies considerably among cancer types, the only way to detect a cancer is through screening. Since the chances of curing many cancers increases the earlier it is diagnosed, physicians often recommend screening tests for the early detection of cancer or precancerous conditions well before symptoms develop. However, the results of screening tests are not definitive. They need to be confirmed or disproved with further testing.
In order to be effective, a cancer screening program must at least meet the following criteria:
- The cancer being screened must be common
- There must be a long period of time during which the cancer is detectable in the absence of symptoms, and, ideally, the cancer must remain localized in the primary area during that time
- The screening tests must be accurate, inexpensive, and acceptable to patients
Because screening tests are almost never definitive in themselves, a second test is generally required to confirm (or exclude) the diagnosis of cancer. This follow up test should not be a repeat of the screening test, but should be a more "specific" test, meaning it's less likely to have false results than the screening test. Most confirmatory tests are tissue biopsies: a portion of the questionable tissue is taken and examined under the microscope to determine whether or not cancer is present.
Unfortunately, all of these conditions are not always met. Consider breast and ovarian cancer.
Breast Cancer Screening
Routine mammograms (x-rays of the breast) are commonly recommended for women over 40 years of age. As a screening test, mammograms make sense because they detect an extremely common condition, are relatively inexpensive to perform, and are reasonably sensitive at finding tumors too small to be detected by either you or your doctor.
However, mammograms are not specific. In fact, for a woman whose risk of breast cancer is low (those under age 50, for example, with no family history), a positive mammogram is very unlikely to be cancer. In other words, it is more likely than not a false positive result. It is for this reason that a mammogram, or any screening test for that matter, should never be relied upon to make the final diagnosis of cancer. A biopsy is always required and the utility of a mammogram is that it directs the biopsy to the proper spot.
Ovarian Cancer Screening
Unlike breast cancer, there is no effective screening test for ovarian cancer. Routine screening currently takes place during the gynecologic exam, which is not very sensitive at detecting small tumors. Another approach would be to perform an invasive procedure called a laparoscopy on essentially all women, which would be entirely impractical due to the expense and risk involved. Fortunately, ovarian cancer is relatively rare, especially when compared to breast cancer.
It turns out that there are only a handful of cancers—breast, cervical, skin, prostate, colorectal—for which useful screening tests exist.
There is disagreement among medical groups regarding the appropriate timing and frequency for some of the screening tests.
Below are recommendations for the American Cancer Society (ACS) for routine cancer screening in people at average risk (same as the general population) for cancer. Other organizations may have different recommendations. People at higher risk (those with a family history, for example) should generally be screened earlier and more frequently. Speak with your doctor about the appropriate screening schedule for you.
Not recommended on a routine basis (because of the frequency of false negative tests, even in carefully selected populations)
Rectal and Colon cancer
Fecal occult blood test
Yearly after age 50
Sigmoidoscopy with or without barium enema
Every 5 years after age 50
Double-contrast barium enema
Every 5 years
Every 10 years after age 50
Discuss with doctor the blood test for prostate specific antigen with or without a digital rectal examination
Yearly after age 50, Men at high risk should begin screening at 45
Cervical, Uterine, and Ovarian Cancers
Every 1 to 3 years between the ages of 18 and 40, then yearly after age 40
Every 3 years for ages 21-29
Every 5 years for ages 30-65 if having both Pap test and the human papillomavirus (HPV) test (or continue to have the Pap test every 3 years)
May be able to stop these screening tests at age 65
Monthly after age 20
Breast physical examination
Every 3 years between ages 20 and 40, then yearly
Yearly beginning at age 40; some protocols suggest every 1-2 years depending on the relative risk status of the patient
Risks of Screening
As with all things, the potential benefits of cancer screening must be weighed against the potential harms. False-positive results for example, can create undue psychologic stress, and if they occur often, can produce unacceptable numbers of unnecessary invasive, expensive and painful diagnostic tests. And even a true positive result may not always be in a patient’s best interest. Because of its slow growth, for example, prostate cancer may never have harmed an elderly man who was successfully screened with the prostate-specific antigen (PSA) blood test. But now that he has the information, he may feel compelled to undergo an aggressive course of treatment to remove the tumor.
Screening tests can also produce false-negative results . This occurs when a screening test fails to detect cancer that is actually present. A false-negative screening test may mistakenly reassure you that you are free of cancer and need not pay close attention to early clinical signs or symptoms. For these reasons, physicians need to be careful when ordering and interpreting screening tests for cancer. This is also the reason that the same screening test should not be repeated to confirm the presence of the cancer it implicates.
Because a diagnosis of cancer must always be made with as much certainty as possible, positive screening test results are insufficient for clinical decision making. A biopsy is required to definitively diagnose cancer. To learn more about how cancer is diagnosed, see the cancer diagnosis section of this classroom.
When cancer is confirmed, staging tests are used to determine whether it has spread to other parts of the body. This information helps doctors choose the appropriate treatment approach for your cancer and to determine your prognosis. To learn more about how cancer is staged, see the cancer staging and grading section of this classroom.
Physicians use genetic tests to detect the presence of genetic mutations that may signal the presence or the risk of a disease or disorder. Genetic testing serves a number of purposes. For example, it has long been used to screen newborn children for genetic disorders. It also allows couples to determine the risk for passing on an inherited disorder to their children. To learn more about genetic mutations, see the cancer genetics section of Cancer 101.
A more recent innovation for genetic testing is its use in estimating the lifetime risk of developing certain cancers in adults. For example, women who carry one of two BRCA gene mutations have an 85% risk of developing breast cancer during their lifetime. This compares to a lifetime risk of approximately 12% in the general population. However, since this mutation only accounts for about 5% of breast cancers, it is not an appropriate screening test for the vast majority of women. It is, however, an appropriate test for patients who have a strong family history of breast cancer.
Despite the fact that more and more genetic screening tests for cancer risk are being developed and marketed, they are not without their controversy. Questions remain about who should have access to genetic information and how this information should be used. If you have a strong family history of cancer, you may wish to speak with your doctor about the risks of benefits of genetic screening.What are the signs and symptoms of cancer?How is cancer diagnosed?What is staging and grading?How is cancer treated?Can cancer be prevented?What are some other cancer resources I can use?
- Reviewer: Igor Puzanov, MD
- Review Date: 09/2012 -
- Update Date: 00/92/2012 -