How Accurate Are Mammograms?

A mammogram is an excellent tool for finding breast cancer, particularly in women age 50 and over. Breast cancer is accurately diagnosed through mammography in about 78 percent of all women tested, while diagnostic accuracy rises to about 83 percent for women over 50. Today’s greatly improved mammograms can usually detect breast abnormalities before they can be felt in a breast exam.
July 6th, 2015

A mammogram is an excellent tool for finding breast cancer, particularly in women age 50 and over. Breast cancer is accurately diagnosed through mammography in about 78 percent of all women tested, while diagnostic accuracy rises to about 83 percent for women over 50. Today’s greatly improved mammograms can usually detect breast abnormalities before they can be felt in a breast exam.

The American Cancer Society recommends that all women get an annual mammography starting at age 40, though the U.S. Preventive Services Task Force (USPSTF) suggests a baseline mammogram at 40 and starting yearly testing at 50. Other issues such as family history come into play, and you should check with your health care provider to determine how often you should be tested.

While the test misses few cancers and is an invaluable diagnostic tool, it does produce a number of false positives, about 6-8 percent, meaning the test can find a reading that looks like cancer but is not. This brings the need for further testing and causes needless worry; however, this temporary trouble is definitely outweighed by the test’s life-saving identification of so many cancers. On the other, more dangerous, side of the coin are the estimated 17 percent of breast cancers missed by mammography. The number may rise as high as 30 percent for women with dense breasts, making the inclusion of clinical breast exam in overall diagnosis even more important. Combining mammography with clinical exam found about four percent more cancers than just mammography.

One of the major factors affecting accurate reading of mammography is breast density, which can be either genetic or brought on by other factors, including postmenopausal hormone usage. Approved for short-term relief of uncomfortable menopausal symptoms, hormone usage can both increase the risk of breast cancer and increase the difficulty of reading mammograms due to increased density of the breasts. Because readings may appear abnormal, women with dense breast tissue may need more follow-up testing. In fact, there is only about a fifty percent chance that a tumor will be detected in their breast prior to being noticeable in a physical exam. If your health care provider tells you that you have dense breast tissue, you may want to ask about having a screening ultrasound in addition to a mammogram. The two tests work in concert to provide more reliable breast cancer screenings for women with dense tissue.

If your radiologist and physician suspect breast cancer, you may be required to have follow-up testing, including diagnostic mammography, breast ultrasound and/or needle biopsy. Rest assured that most of these findings are found to be normal breast tissue or benign tissue. You may be sent to get a diagnostic mammogram, which differs from screening mammograms in that it focuses only on the abnormal area, giving a much higher quality image of suspected trouble. If definitive results are not found, you may go on to have a breast ultrasound, while women at very high breast cancer risk may benefit from having a breast MRI as well.

Images that call for further study include masses or lumps with a smooth, well-defined border. While most of these are non-cancerous, an ultrasound will let the doctor know what is inside the mass, a critical point in identifying the mass; for instance, cysts are seen to contain fluid. A mass with a star-burst appearance or irregular appearance is more likely to be cancerous and you may be sent immediately for a needle biopsy. Sometimes abnormalities called microcalcifications are found, small deposits of calcium which may be benign or cancerous and often require a biopsy.

Use of breast ultrasound has dramatically improved breast cancer diagnosis accuracy. According to a study in the Journal of the American Medical Association (AMA) combining the two tests brings the diagnostic success rate to about 75 percent. Particularly if your health care provider tells you that you have dense breast tissue, you may want to ask about having a screening ultrasound in addition to a mammogram. The two tests work in concert to provide more reliable breast cancer screenings for women with dense tissue. Unfortunately, breast ultrasound is not available everywhere, partially because of low Medicare reimbursement on the procedure.