What is the best test for breast cancer screening?

A bird on a fall day. (Dr. Noorali Bharwani)
A bird on a fall day. (Dr. Noorali Bharwani)

Is MRI test better than mammography for early detection of breast cancer?

This question applies to women who are at average risk of breast cancer. They have no personal or family history of breast cancer. The controversy over the best way to screen for breast cancer among women at average risk continues.

Regular screening for breast cancer with mammography, breast self-examinations and clinical breast examinations are widely recommended to reduce mortality due to breast cancer.

Unfortunately, the available evidence does not support the use of MRI scans, clinical breast examination or breast self-examination to screen for breast cancer among women at average risk. But we continue to use these investigations.

Recent publications have again questioned the use of MRI alone or in combination with mammography for breast screening. There are more false-positives resulting in more negative biopsies.

Some researchers (JAMA Intern Med. 2018 Apr 1) have concluded that screening with MRI is not for everyone. Women who undergo breast cancer screening with MRI are much more likely to be referred for biopsy – that will ultimately be negative – than if they have screening mammography alone.

The authors of the article warn, “This is even true of women with a personal history of breast cancer. The benefit of possible early detection of breast cancer with MRI has to be carefully weighed against unnecessary additional diagnostic manoeuvres.”

Other authors have concluded that more studies are required to identify women who will benefit from screening MRI to ensure an acceptable benefit-to-harm ratio.

The experts have to determine whether a screening test would benefit or harm the patient. There is risk of harm and cost of false-positive results, overdiagnosis and overtreatment. How many unnecessary biopsies will be done to find one cancer? How many women will have to anxiously wait for days, weeks or months to find out if they have cancer? Not easy questions to answer unless you are sailing in the same boat.

Any positive result from screening has emotional costs such as anxiety and worry for patients and their families, and financial costs to both the patient and the health care system as a result of additional and potentially unnecessary diagnostic tests.

For women with positive results on screening tests, additional diagnostic tests will usually be recommended, such as further mammography, ultrasound and/or tissue sampling with core needle biopsy.

You may ask, “Doctor, what is the best way to screen asymptomatic women with no personal or family history of breast cancer?” The answer lies in the following recommendations from the Canadian Cancer Society:

If you are 40–49: Talk to your doctor about your risk for breast cancer, along with the benefits and potential risks of mammography. The benefits of regular mammography to screen for breast cancer in women younger than 50 are still unclear.

If you are 50–69: Have a screening mammography every 2 years.

If you are 70 or older: Talk to your doctor about how often you should have a mammography.

There is some radiation involved in having mammography. The benefits of mammography and finding breast cancer early outweigh the risk of exposure to the small amount of radiation received during mammography.

Now, here is the good news. The average 5-year survival rate for people with breast cancer is 90 per cent. The average 10-year survival rate is 83 per cent. If the cancer is located only in the breast, the 5-year relative survival rate is 99 per cent. Sixty-two percent of cases are diagnosed at this stage.

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