Essentially, no cancer produces signs or symptoms at the beginning. During this period, the only way to detect a cancer is through screening. Since the chances of curing many cancers increases the earlier it is diagnosed, doctors recommend screening tests for certain cancers and for people at higher risk. However, the results of screening tests are not definitive. They need to be confirmed or disproved with further testing.
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 tissue is taken and examined under the microscope to determine whether or not cancer is present.
Screening tests are developed for common cancers that have a long period of development before symptoms develop. The tests also need to be accurate and acceptable to people in order for them to be effective part of medical care. Unfortunately, all of these conditions are not always met. Consider breast and ovarian cancer.
Breast Cancer Screening
Routine mammograms are commonly recommended for women over 40 years of age since the risk of cancer increases with 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 with no family history), a positive mammogram is very unlikely to be cancer. 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.
Ovarian Cancer Screening
Unlike breast cancer, there is no effective screening test for ovarian cancer. A technique called a laparoscopy could do screenings but it is an invasive procedure. It is also impractical because of the risk and expense involved. Since ovarian cancer is relatively rare this screening is not considered practical and not widely used.
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 of average risk (same as the general population) for cancer. Other organizations may have different recommendations. People at higher risk, such as those with a family history, should generally be screened earlier and more frequently. Speak with your doctor about the appropriate screening schedule for you.
Colon and rectal cancers (one of the following)
Fecal occult blood test
Yearly starting at age 50
Sigmoidoscopy with or without barium enema
Every 5 years starting at age 50
Double-contrast barium enema
Every 5 years
Every 10 years starting at age 50
Talk with your doctor about the risks and benefits of the prostate-specific antigen (PSA) blood test with or without a digital rectal examination
Yearly starting at age 50, Men at high risk should begin screening starting at age 45
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)
Women over age 65 with a history of normal test results may permanently stop cervical cancer screening
Breast self-examination (BSE)
BSE can be done monthly for women starting at age 20. Report any abnormalities to your doctor.
Breast physical examination
Every 3 years between ages 20 and 39, then yearly starting at age 40
Yearly beginning at age 40; some protocols suggest every 1-2 years depending on the relative risk status of the woman
Other Screening Tests
Other screening tests are available, but they have not been shown reduce cancer deaths, unlike some recommended screening tests. Testing may be done for those who are in a high risk group, like someone with specific genetic markers or Barrett's esophagus. Talk to your doctor about your risk and how often you may need to be tested.
Tests may include:
- Blood tests—Blood tests help determine levels of specific proteins in the blood that are elevated in the presence of cancer. Examples include, CA-125 (ovarian) or alpha-fetoprotein (liver).
- Breat MRI scan and/or transvaginal ultrasound—Women who carry the genetic mutation BRCA1 or BRCA2 have a high risk of breast, ovarian, or uterine cancers. Regular testing may help detect abnormalities earlier.
- Skin exams—May help detect abnormalities of the skin, such as changes in color shapes of moles, which increase the chance of skin cancers (especially melanoma). This may be done yearly or at regular checkups. Your doctor may advise you to check your skin at home once a month.
Risks of Screening
As with all things, the potential benefits of cancer screening must be weighed against the potential harms. False-positive results, tests indicate cancer when there is none, can create undue psychological stress. They can also lead to unnecessary invasive, expensive, and painful diagnostic tests. Even an accurate test, may not always be in a person’s best interest. For example, prostate cancer often grows slowly. It may never have harm elderly men before they die of natural causes. A positive test, though accurate may compell someone to undergo an unnecessary, aggressive course of treatment to remove the tumor.
Screening tests can also produce false-negative results, the test fails to detect cancer that is actually present. A false-negative screening test may mistakenly reassure someone that they are free of cancer and need not pay close attention to early signs or symptoms.
Diagnosis of cancer must always be made with as much certainty as possible. For this reason, positive screening test results alone are not enough for a diagnosis. A biopsy is required to definitively diagnose cancer. To learn more about how cancer is diagnosed, see the cancer diagnosis section of this classroom.
Doctors use genetic tests to detect the presence of genetic mutations that may signal the presence or the risk of a disease or disorder. The genetic changes that are associated with specific cancers were determined by testing genes of people who have had that cancer and families who have high risk of cancers.
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 those 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. To learn more about genetic mutations, see the cancer genetics section of Cancer 101.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: Mohei Abouzied, MD, FACP
- Review Date: 03/2015 -
- Update Date: 05/12/2015 -