A Mammogram Was Not Enough For Me
I am a radiologist and I specialize in breast imaging. My own breast cancer was missed by mammography and diagnosed through additional screening. When is a mammogram not enough?
I had my annual mammogram as well a 3D mammogram (known as tomosynthesis or tomo). I was relieved when both tests appeared “normal.” However, because I have both dense breasts and a family history of breast cancer, I used a breast cancer risk assessment tool to determine my lifetime risk of developing cancer. I discovered my risk to be 20% (“normal” risk is about 11% at my age). Based on that risk, I chose to have additional screening with MRI. MRI showed a suspicious mass that was easily seen by ultrasound to guide biopsy, revealing an invasive breast cancer that, because it was detected early, had not yet spread to lymph nodes. Fortunately, I was able to be treated with lumpectomy and radiation and did not need chemotherapy. I am glad I had the information I needed to choose extra screening.
I want to empower other women and their physicians to understand screening options and risk factors so that they too can make informed decisions on these important issues.
The purpose of screening is to detect cancer earlier than it would otherwise be found. When cancer is found early, outcomes are better and less aggressive treatment is needed. For breast cancer, mammography does a modest job at achieving these goals, producing a 15% drop in deaths due to breast cancer when women in their forties are screened regularly and a 22% drop in deaths among women aged 50-74 similarly screened. A downside to mammography is that about 10% of women screened will be recalled for additional testing (usually just a few more mammographic images or ultrasound) and 1-2% of women screened will be recommended for needle biopsy after such extra testing. Overall, only about 5 women in 1000 (0.5%) will be found to have cancer.
There are several reasons mammography does not produce greater benefits:
- Not all women go for mammograms (some by choice).
- Women younger than age 40 are only recommended for mammography when they have very high risk or symptoms.
- Some medical societies leave it up to women to decide whether or not to have mammograms from age 40-50.
- In women who do have mammograms regularly, dense breast tissue is a common reason that cancer may go undetected.
What are false positives and why do they matter?
False positives (when a test indicates something may be cancer which turns out not to be) are an inevitable part of screening. The only way to know whether or not something detected is cancer is by conducting additional tests and/or biopsy. Importantly, the likelihood of a false positive decreases after the first year of any test (as comparison can now be made to previous findings). 3D-mammography (tomosynthesis) slightly improves cancer detection and reduces the chance of recall for noncancerous findings, but it is still far from a perfect test.
Do you know your risk?
Risk increases with age, so it is important to know and reassess risk factors yearly. Various models are used to estimate risk.* Two examples are:
- The Gail model (http://www.cancer.gov/bcrisktool/) is used to determine risk when medications such as tamoxifen may be recommended. Note that the Gail model does not factor in age at diagnosis of relatives and should not be used to determine risk for purposes of deciding on MRI screening.
- The IBIS model (http://www.ems-trials.org/riskevaluator/): A lifetime risk of 20% or higher is considered “high risk”. Women who are at high risk for breast cancer because of family/genetic history should start screening by age 30 and should include MRI as part of their annual screening. This is true regardless of breast density.
* It is important to be aware that no risk models in current widespread use factor in breast density. Regardless of other risk factors, women with the densest breasts are 4 to 6 times more likely than women with fatty breasts to develop breast cancer.
What other screening modalities are available?
MRI requires lying face down on a support in a relatively closed tunnel and injection of intravenous contrast. MRI will show cancers not seen on mammography in at least 10 of every 1000 women screened. Follow-up testing including biopsies for false positives occur in 6% to 12% of women. Invasive and in situ cancers are well seen on MRI and are not hidden by dense tissue.
Ultrasound does not require any injection or ionizing radiation. Ultrasound can be performed by hand or by “automated” systems. Follow-up ultrasound is needed in about 13% of women after automated ultrasound. One downside to ultrasound (either by hand or automated system) is that it has a relatively high false positive rate. On average, ultrasound will allow detection of another 2-4 cancers per 1000 women screened beyond those seen on mammography. Invasive cancers are well seen and are not hidden by dense tissue.
Under development: Contrast-enhanced mammography (which involves injection of a contrast agent) and molecular breast imaging (involves injection of radioactive material) are methods predominantly used in research at this time.
There are benefits and considerations for each type of screening technology and you should discuss what is right for you, based on your personal risk factors, with your health care provider.