Mammograms: the good, the bad and the ugly

There are few rites of passage for women in the United States that are as fraught with emotion and controversy as mammograms.

All women in the US aged 50-74 should receive a screening mammogram every two years, according to the U.S. Preventive Services Task Force.

The American Cancer Society recommends that average-risk women begin annual mammograms at age 45, shifting to every other year screening at age 55 if desired.

Donald Berry, PhD, a statistician at the M.D. Anderson Cancer Center in Houston, “believes that the benefits of screening mammography are likely very modest in women under the age of 60.”

Once upon a time, the recommendation was that everyone begin at age 40. In fact, the Affordable Care Act requires that insurance cover screening mammography every 1–2 years for women age 40 and over with no copayments, coinsurance, or deductibles.

Why the change?

The best cancer tools would detect breast cancer at a stage early enough that patients could be completely cured. In a perfect world, the tools would detect abnormal cells before they become cancer cells so that they could be removed.

Mammography, which is an x-ray of the breast, is an imperfect tool.

The most optimistic estimates from observational data indicate a 63% reduction in death from breast cancer in women who are regularly screened with mammograms every 1-2 years. Screening trial data suggest a more modest but significant reduction, with the results of individual studies ranging from no effect to a 45% reduction in breast cancer deaths. Mammography is imperfect because it does not reliably detect lesions before they are cancerous (emphasis added).

It can also be a painful tool, because the breast must be squeezed tightly between two plates in order to produce good x-ray images.

In making the recommendation to reduce screenings for women of average risk, researchers note the number of false positives: mammograms that look abnormal but are, in fact, normal. False positives can lead to additional imaging as well as biopsies. Most women who have biopsies have benign results.

False negatives are mammograms that look normal but are, in fact, abnormal. This yields a false sense of security for patient and doctor. Screening mammograms do not see about 20% of breast cancers that are present at the time of screening.

A small percentage of false-negatives are cancers that are mammographically occult.

A 2016 report on 405,191 women in the US, aged 40-89, who were screened with digital mammography between 2003 and 2011, revealed the following:

  • Recommendations for additional imaging: 124.9 per 1,000 women
  • Rates of false-positive results: 121.2 per 1,000 women
  • Recommendations for biopsy: 15.6 to 17.5 per 1000 women
  • Rates of false-negative results: 1.0 to 1.5 per 1,000 women. False-negative rates were highest for women with extremely dense breasts in all age groups except age 60-69.

Sometimes the breast cancer grows so fast that it appears within months of a negative mammogram. This is not a false negative.

For 2-of-5 women diagnosed with breast cancer, the disease has spread from the breast to the lymph nodes or it has metastasized elsewhere in the body. For these women, mammography was truly an imperfect screening tool.

How are mammography facilities regulated?

The federal Mammography Quality Standards Act (MQSA) requires mammography facilities across the nation to meet uniform quality standards. All facilities must

  1. be accredited by an FDA-approved accreditation body;
  2. be certified by the FDA, or an agency of a state that has been approved by the FDA, as meeting standards;
  3. undergo an annual MQSA inspection; and
  4. prominently display the certificate issued by the agency.

Digital mammography has replaced film in the United States.

Three-dimensional (3-D) mammography, also known as digital breast tomosynthesis (DBT), has not yet been shown to be “superior to 2-D mammography at identifying early cancers and avoiding false-positive results.”

There are other screening methods, in particular MRI and ultrasound. Additional methods under development include a 3D ultrasound and a breast CT scanner (bCT) that allows radiologists to view the breast in three dimensions and has the potential to see tumors obscured by dense breast tissue.

Until we have better screening tools, women who are at higher risk — through family history, genetic profile, dense breast tissue, biopsies showing elevated risk — should have mammograms more frequently, perhaps supplemented with ultrasound or MRI screening as well.

The real challenge is to identify breast cancer at an early stage in women between ages 30 and 49, because they account for 40% of all breast cancer mortality.

 

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