Understanding your Mammogram

Every two minutes in the United States, a woman is diagnosed with breast cancer. It is the most common cancer in women other than skin cancer. The good news is that since about 1990, the chances of surviving breast cancer are continuing to improve, probably due to early detection, increased awareness and improved treatment techniques.

The cornerstone of early detection methods for breast cancer is the mammogram.  Basically, a mammogram is a low-dose x-ray to look for changes in breast tissue which could indicate a small breast cancer. Small breast cancers found on mammogram are the easiest and most successful to treat.  Most commonly, the test is done as a “screening” mammogram, which takes pictures of the breast from two different angles, and is used to look for signs of breast cancer in women without symptoms or problems.

Another type of mammogram is called a “diagnostic” mammogram, which is used to look at the breast in someone who has symptoms or changes in the breast that were seen on the screening mammogram. This type of mammogram may include extra angles or views of the breast.

Mammogram x-rays are taken on a machine designed to look only at breast tissue, and one that uses lower doses than usual x-rays. These x-rays don’t pass through tissue easily, so the mammogram machine has two plates that compress the breast to spread the tissue apart. 

When mammograms were first developed, they were typically printed on large sheets of film. Today, digital mammograms are much more common. These are recorded and saved in files in a computer, and are also known as “full-field digital mammography” (FFDM).  A newer type of mammogram is known as “breast tomosynthesis” or 3D Mammography, which is available at Lompoc Valley Medical Center.

In this type of mammogram, the breast is compressed once and the machine takes multiple low dose images as it moves over the breast. The computer then puts the images together as a 3-dimensional picture. This type of mammogram may use more radiation than a standard mammogram, but may show the breast tissue more clearly. There is evidence that tomosynthesis may be better at finding more cancers, and may also lower the chances of getting “called back” after your mammogram because of uncertain findings. Not all insurance companies cover this type of mammogram yet. 

Many patients ask if mammograms are safe. Although mammograms use a small dose of radiation, the benefit of finding a cancer early outweighs any potential harm from the radiation exposure. An average total dose of radiation from a typical mammogram is equivalent to what people living in the United States would be exposed to just in their environment (known as “background” radiation) in an 8-week period of time.

When you and your doctor receive your mammogram report, your results will be categorized using a number system of 0 through 6, which is called a BI-RADS assessment category (Breast Imaging Reporting and Data System). This is done to help accurately communicate the meaning of the results and the recommendations for follow-up. A BI-RADS category of 0 means that the images may not have been clear and the radiologist needs additional evaluation to make a determination. A category of 1 means nothing abnormal was found, and a category of 2 means that there were some “benign” or non-suspicious findings, but also nothing “abnormal.” A BI-RADS category 3 means that there is a finding in the images that is probably benign, but it may be helpful to follow the change over time to confirm that it is benign. This category often comes with a recommendation for repeat imaging in 6 months and continuing regularly. Findings in this category have a higher than 98 percent chance of being benign. Placing findings in this category can help to avoid unnecessary biopsies. 

Category 4 means that there is a suspicious abnormality that may NOT be a cancer, but could be. The rating means that a radiologist is concerned enough to recommend a biopsy. A category 5 classification means that the findings look like a cancer and have a high chance (greater than 95 percent) of being cancer, with a biopsy being strongly recommended. BI-RADS 6 is a finding that has already been proven to be a cancer by previous biopsy.

The mammogram report will also report whether or not you have “dense” breast tissue. Dense breast tissue is normal and very common. It means that there is a lot of fibrous or glandular tissue in the breast, and not much fat. Often breasts become less dense, or more fatty, with age. Breast density is something that is seen on the mammogram images, and does not mean that the breast is firm to the touch.

The BI-RADS system also categorizes breast density on the mammogram into 4 categories based on the degree of density seen, and in California your mammogram report will tell you if your mammogram showed either heterogeneously dense or extremely dense (level 3 or 4 in the categories) breast tissue.

Breast density is important because women with dense breast tissue seem to have a slightly higher risk of cancer and dense breast tissue also makes it harder to find a cancer on the mammogram. Both dense breast tissue and cancers look white on the mammogram image (in a black background), so a cancer can “hide” in a dense area of tissue.  Women with dense breasts still need mammograms, because most cancers can still be found. It is still a matter of debate what additional tests, if any, women should have if their breasts are dense. Both ultrasound and magnetic resonance imaging (MRI) can help find some breast cancers, but these imaging techniques also show more findings that may lead to unnecessary biopsies.

If your mammogram report showed dense breast tissue, talk with your doctor about what this means for you. It may be recommended that women at higher risk undergo more testing. 

Some women are alarmed when they are “called back” after their mammogram for additional tests. Getting “called back” is actually very common and fewer than 1 in 10 women who are called back for more tests actually have cancer. The call back could be because the pictures weren’t clear, the tissue was dense, or there is an area in the breast that just looks different. At the call-back appointment, you may have additional mammogram x-rays, or an ultrasound, or it may be recommended that you have an MRI. You will be told at the visit if the findings turned out to be nothing to worry about, whether your next mammogram should be any sooner than normal, or whether you should have a biopsy. 

Although mammograms are the best screening tests we have for breast cancer at this time, they are not perfect. Screening mammograms may miss up to 20 percent of breast cancers. Also, sometimes changes on a mammogram look worrisome even though a cancer is not present. This is called a “false positive” result and may lead to more testing.  Mammograms save lives by detecting more breast cancers at an earlier stage when the cancers are more curable. However, for each breast cancer death prevented, there may be 3-4 women “over-diagnosed,” meaning a false positive test, or detection of a cancer that might never have affected a woman’s health. For that reason, some organizations, such as the U.S. Preventive Services Task Force (USPTF) have recommended starting mammograms a little later (age 50). The American Society of Breast Surgeons, however, believes that the life-saving benefits of screening mammography outweigh any other considerations, and recommends:

• Women at average risk of breast cancer should start annual mammograms at age 40
• Women with a formal risk assessment showing a 20 percent or greater lifetime risk should start annual mammogram at age 35, and supplemental imaging as recommended by their doctors
• Women with a known genetic mutation or history of radiation to the chest should receive an annual MRI starting at age 25 and annual mammograms starting at age 30
• Women should continue annual mammograms until their life expectancy is less than 10 years
• All women should have screening with tomosynthesis (3D mammograms).

Mammograms are a simple but effective way to minimize your risk from breast cancer!