Breast Cancer Screening: Benefits and Harms

Breast cancer is the second most common cancer among women in the United States.

Screening for breast cancer means looking for signs of breast cancer in all women, even if they have no symptoms. The goal of screening is to catch cancers early. Early-stage cancers are easier to treat than later-stage cancers, and the chance of survival is higher. Routine screening for breast cancer lowers one’s risk of dying of breast cancer.

Screening for breast cancer is done by mammography. A mammogram is a special series of x-rays taken of the breast. A doctor looks for any abnormal signs or patterns on the mammogram that might be breast cancer. These signs usually show up on the mammogram before any lump can be felt in the breast. If there is anything unusual on the mammogram, more tests have to be done. These tests can include another mammogram, an ultrasound, or a biopsy. Studies have shown that women who have routine mammograms have 10% to 25% less chance of dying of breast cancer than women who do not have mammograms.

In the United States, the US Preventive Services Task Force recommends that women aged 50 to 74 years get a screening mammogram every 2 years. For women younger than 50 years, some women may choose to be screened, but not all women need to be. This depends on several factors, as discussed below.

Mammograms are not perfect tests. Some cancers are missed by a mammogram. On the other hand, sometimes mammograms find things that look like cancer but turn out not to be cancer. This is called a false-positive result. False-positive mammogram results lead to more testing, which is time consuming and can cause unnecessary anxiety. On average, among all 50-year-old women who start breast cancer screening, more than half will have a false-positive mammogram result over the next 10 years.

Another possible harm of screening is overdiagnosis. This means finding something on a mammogram that is breast cancer or has a chance of becoming breast cancer, but is such a low-risk type of tumor that it would never have caused any health problems if left alone. Instead, because it was found on mammogram, standard cancer treatment, such as surgery and radiation therapy, is recommended. In cases of overdiagnosis, these treatments are unnecessary and costly and can have both physical and psychological side effects. It is difficult to know exactly how often overdiagnosis happens, but some studies estimate that 1 in 5 breast cancers found on mammograms are overdiagnosed and lead to unnecessary treatment.

The pros and cons of breast cancer screening are different for every woman. Age is an important factor. Even though the general recommendation is to start screening at 50 years of age, for women at higher risk (such as those who have breast cancer in their family), it may be a good idea to start screening at a younger age. Each woman also has different personal values, especially toward the idea of unnecessary medical tests and treatments.

Talk to your doctor if you are younger than 50 years and have questions about whether you should get a mammogram.

Sources: US Preventive Services Task Force

Pace LE et al. A systematic assessment of benefits and risks to guide breast cancer screening decisions. JAMA. 2014;311(13):1327-1335.

Topic: Preventive Medicine