Reasons for False-Positive & False-Negative Results

Let's start out with an important, but often suprising fact - initial mammograms by themselves are usually not enough to determine the existence of a benign or malignant disease with absolute certainty. Here's why...



Reasons for False-Positives Results

False-positive readings on a mammogram occur when cancer is NOT present, but the mammogram was read as abnormal. Many, but not all of the reasons that may cause the abnormality are as follows.

tinted CC mammogram in blue from Two Views

Dense breast tissue.

Dense breast tissue is most often seen in younger, pre-menopausal women; in pregnant or nursing women; and in post-menopausal women undergoing hormone therapy. The radiologist may not be able to see through the dense tissue on the typical two mammographic views per breast and may ask you to come back for additional mammogram views.

Calcification.

This is a tiny deposit of calcium within the breast tissue that looks like a small white spot on the X-ray film. A calcification can be an early indicator of a type of breast cancer known as DCIS, or ductal carcinoma in situ. Or it can be a benign calcium deposit that amounts to nothing more than a fibrocystic change in your breast, aging arteries, inflammation, or evidence of past injuries to the breast. Your doctor may ask for additional mammogram views to see if your calcification is benign, meaning its edges are round and smooth. If the edges are lacy and branched out, or if the calcification is a new finding after several years of uneventful mammograms, your doctor may want to do a needle biopsy, which involves inserting a needle to remove tissue or fluid for analysis. In some cases, particularly if the calcification is close to the chest wall, a surgical biopsy may be necessary, requiring the surgeon to make an incision in the breast and remove the abnormal area.

Cysts or other masses.

Cysts are benign, usually fluid-filled sacs, whereas a true breast cancer tumor is solid. The difference is not apparent on first glimpse. If your doctor sees any kind of mass on your mammogram results, you may be called back in for additional views; your breasts will be pressed down and viewed to see if the mass goes away, which means it was simply dense tissue. If your doctor still sees a mass, you may be asked to have an ultrasound exam, which can discern the difference between a fluid-filled sac and a solid tumor. Even then, an ultrasound may not be conclusive because not all solid masses are tumors. It may be a fibroadenoma, which is a benign (non-cancerous) tumor. But if your doctor sees a solid mass on your ultrasound, you may be scheduled for a biopsy. Sometimes a mass may be part solid and part fluid, and your doctor may want to repeat your mammogram in a few months to see if it’s changed.

Every body is different.

Remember every woman’s body is different, so interpretations of mammograms can often be difficult because a ‘normal’ breast can appear differently for each woman. Also, the appearance of an image may be compromised if there is powder or salve on your breasts or if you have undergone breast surgery. In some cases, it may just be an area of thicker or more dense tissue in your breast.

It may help to know that studies and research have found that of every 1,000 U.S. women who are screened, five percent to 15 percent require more testing such as additional mammograms or ultrasound. And it is estimated that a woman who has yearly mammograms between ages 40 and 49 has about a 30 percent chance of having a false-positive mammogram at some point during that time period. These are NOT the same statistics as statistics that show cancer. They are simply numbers that have been given to show how frequently a false-positive result may happen.

Radiologists or doctors that see something on a mammogram that they feel is abnormal will most likely ask the patient to come back at a later date to take more mammogram images. If you are told that your mammogram is abnormal or that there is a "spot" on your mammogram, as hard as it may be, doctors urge that you should NOT panic. This does not always mean you have something as extreme as breast cancer.







Reasons for False-Negative Results

Mammograms also have a history of missed tumors, or "false-negatives." It is hard to obtain truly accurate data regarding the number of false negatives for a host of reasons that statisticians could never be able to control.

Estimates of false-negative depend on close follow-up of a large number of patients for many years. However, it is commonly agreed that false-negatives are more common in younger women than in older women.

mammogram tumor in Two Views

False-negatives can sometimes be attributed to dense tissues obscuring the cancer and/or the appearance of cancer on a mammogram has a large overlap with the appearance of normal tissues.

As with false-positive results, it's important to remember every woman’s body is different, so interpretations of mammograms can often be difficult because a ‘normal’ breast can appear differently for each woman. Also, the appearance of an image may be compromised if there is powder or salve on your breasts or if you have undergone breast surgery. In some cases, it may just be an area of thicker or more dense tissue in your breast. It may also be a cyst, or a benign lump such as a fibroadenoma.

There are many other reasons as well, including errors by the observer. And it is important to find a qualified mammography radiologist and technologist that can perform your test or tests. It is equally important that these results are read by a qualified radiologist.


Learn more about
false-positive and false-negative mammogram results.

mammogram reasons for results in Two Views






IMPORTANT: The information on this page, and throughout the entire site, is not intended to provide advice or treatment for a specific situation. Consult your physician and medical team for information and treatment plans on your specific condition(s). Images are shown for illustrative purposes. Do not attempt to draw conclusions or make diagnoses by comparing these image to other medical images, particularly your own.








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