The earlier a cancer is diagnosed, the better the patient’s chances of survival. For instance, a woman whose breast cancer is diagnosed an early stage has a 93-100% chance of surviving five years, according to the American Cancer Society. However, someone diagnosed with a very advanced case has just a 22% chance of surviving the same amount of time.
Generally speaking, there are two broad categories of medical tests that detect cancers. Screening tests look for signs of cancer in patients that currently present no symptoms. Diagnostic tests investigate symptoms of cancer that are already present and are used to make a diagnosis. The actual medical tests may be the same—for example, a woman who feels a lump in her breast will undergo a diagnostic mammogram, not a screening mammogram.There are several main types of cancer screening tests.
Imaging Tests
- CT (computerized tomography) scans, x-rays, and mammograms (breast x-rays) take 2- or 3-D pictures of the inside of your body to look for abnormal growths or changes. Imaging tests are an effective for finding abnormalities, including cancers.
- CT scans have higher levels of radiation than x-rays or mammograms, and are most often used to screen for lung cancer in high-risk individuals for whom the benefit of finding deadly lung cancers outweighs the radiation risks. Radiological scans—including mammograms, x-rays, and CT scans—expose you ionizing radiation, which is a risk factor for cancer.
- MRIs use magnets and radio waves instead of radiation to create images. MRIs are often used to screen women who have higher-than-average odds of developing breast cancer. (Women with a family history of breast cancer, for instance, would be considered to be at higher risk.)
Blood and Other Lab Tests
Blood tests look for specific substances in the blood that may indicate the presence of disease. The most common cancer screening blood tests include the CA-125 (ovarian cancer), alpha-fetoprotein (liver cancer), and the Prostate Specific Antigen (prostate cancer). There’s also the fecal occult blood test, which checks the stool for blood to screen for colon cancer. One test that doesn’t require bloodwork is the Pap smear, which looks for abnormalities in samples of cells collected from the cervix. Some of these tests are used in combination with other screening methods.
Invasive Tests
Colonoscopy and sigmoidoscopy use a thin tube with a light and a lens to look inside the rectum and colon for potentially precancerous growths (polyps). If you have polyps, your physician can generally remove them during the same procedure, before they have an opportunity to develop into cancer.
Current Screening Recommendations
The U.S. Preventive Services Task Force (USPSTF), an independent panel of physicians and health professionals, issues medical recommendations based on the most current scientific data every five years. For cancer screenings, the Task Force analyzes the benefits, harms, and realistic estimate of lives saved as a result of screening. Here are the USPSTF’s most current recommendations for common cancer screenings:
- Breast cancer. Women between 50 and 74 should undergo screening mammograms every two years. Women 40 to 49 should make individual decisions about screening based on their risk factors. (The American Cancer Society and other organizations continue to recommend annual screening mammograms beginning at age 40.)
Rajiv V. Datta, MD, an oncologist based in Valley Stream, NY and medical director of the Gertrude & Louis Feil Cancer Center, also advocates a personalized approach to screening for women in their 40s: "Given variations in guidelines between different medical groups for frequency of mammograms, it is highly advised that the test be individualized to the risk of a given patient." - Cancers of the colon and rectum. The USPSTF recommends routine screening for adults 50 to 75 via fecal occult blood tests, sigmoidoscopy, or colonoscopy.
However, "Virtual colonoscopy is considered to be an acceptable option for colon cancer screening in adults older than 50 who have an average risk of colorectal cancer, but not those with a history of polyps or who are considered to be at increased risk for colorectal cancer," Datta, says, adding, "Virtual colonoscopy exposes patients to radiation." - Lung cancer. Adults 55 to 80 who smoked 30 packs of cigarettes per year and currently smoke (or quit smoking within the past 15 years) should undergo low-dose CT scans annually.
- Cervical cancer. Women should have Pap smears (in which cells taken from the cervix are studied under a microscope for signs of abnormalities) every three years between ages 21 and 65, or every five years in combination with HPV (human papillomavirus) testing for women ages 30 to 65. Most cervical cancers are caused by one of the 12 high-risk types of HPV, which are sexually transmitted.
- The USPSTF recommends against routine screening for ovarian and prostate cancer in healthy individuals.
The Downside of Screenings
The benefit of cancer screening is finding a harmful cancer early enough to treat it successfully. However, all screening tests have risks and the potential for harm.
- Some screening tests may cause actual physical harm, such as bleeding or a perforated colon (a tear in the wall of the colon) during a colonoscopy.
- Radiological scans expose you ionizing radiation, a risk factor for cancer.
- Screening tests may incorrectly indicate something is wrong (a false positive), which can lead to additional—and unnecessary—medical procedures and anxiety for patients.
- Screening may miss potentially harmful abnormalities (a false negative).
- Screening tests detect slow-growing cancers that may never cause symptoms or problems; however, individuals undergo additional and unnecessary testing or treatment (overdiagnosis).
You should fully understand the benefits and risks of each cancer screening you’re considering and have realistic expectations about what screening can—and cannot—do.
Does Screening Save Lives?
A recent analysis of the life-saving effect of cancer screening published in the International Journal of Epidemiology concluded, "Among currently available screening tests for diseases where death is a common outcome, reductions in disease-specific mortality [death] are uncommon and reductions in all-cause mortality [death from any cause] are very rare or non-existent." In other words, cancer screening does save some lives, but not as many as we’d like to believe.
Rajiv Datta, MD, reviewed this article.
Sources
Datta, Rajiv, MD. Email to author, April 1, 2015, May 6, 2015.
"Breast Cancer Survival Rates by Stage." American Cancer Society. Page last revised February 26, 2015.
"Cancer Screening." National Cancer Institute. Accessed April 30, 2015.
"Screening Tests." National Cancer Institute. Updated March 24, 2015.
Aschwanden, Christie. "The Case Against Early Cancer Detection." FiveThirtyEight.com. November 24, 2014.
Welch, H. Gilbert, and Brittney A. Frankel. "Likelihood That a Woman With Screen-Detected Breast Cancer Has Had Her 'Life Saved' by That Screening." Archives of Internal Medicine 171, 22 (2011): 2043-2046.
Saquib, N., J. Saquib, and J.P.A. Ioannidis. "Does Screening for Disease Save Lives in Asymptomatic Adults? Systematic Review of Meta-Analyses and Randomized Trials?" International Journal of Epidemiology 44, 1 (2015): 264–277, doi: 10.1093/ije/dyu140.
"Cervical Cancer: Screening." U.S. Preventive Services Task Force. March 2012.
"Draft Recommendation Statement: Breast Cancer: Screening." U.S. Preventive Services Task Force. May 2015.
"Prostate Cancer: Screening." U.S. Preventive Services Task Force. Updated May 2012.
"Colorectal Cancer: Screening." U.S. Preventive Services Task Force. Updated 2008.
"Ovarian Cancer: Screening." U.S. Preventive Services Task Force. Updated 2012.
"Computed Tomography (CT) Scans and Cancer." National Cancer Institute. July 16, 2013.
"Ovarian, Fallopian Tube, and Primary Peritoneal Cancer Screening (PDQ®)." National Cancer Institute. March 27, 2015.
"Prostate-Specific Antigen (PSA) Test." National Cancer Institute. July 24, 2013.
"Colorectal Cancer Screening (PDQ®)." National Cancer Institute. December 11, 2014.
"Breast Cancer Screening (PDQ®)." National Cancer Institute. April 13, 2015.
"Screening For Breast Cancer With Mammography." The Nordic Cochrane Centre. Accessed March 23, 2015.
"Pap Smear." MedlinePlus. Page updated March 11, 2014.
