Mammography for detection of breast cancer does not reduce the number of deaths from the disease and may actually lead to over diagnosis, according to a new study published in JAMA Internal Medicine.
After skin cancer, breast cancer is the most common cancer among American women. Around 231,840 women in the US will be diagnosed with breast cancer this year, and around 40,290 will die from the disease.
As with other cancers, early detection of breast cancer is a key for successful treatment and this can be achieved through breast cancer screening. The main tool used for screening is mammography, allowing clinicians to see any tissue abnormalities.
The US Preventive Services Task Force (USPSTF) recommends that women aged 50-74 have a mammogram every 2 years.
According to the American Cancer Society, death rates from breast cancer have been falling since 1989, and this is partly attributed to earlier detection as a result of screening.
However, study co-author Richard Wilson, of Harvard University in Cambridge, and colleagues note that there is increasing concern that mammography may lead to over diagnosis by “identifying small, indolent or regressive tumors that would not otherwise become clinically apparent,” which means many women may receive treatment they do not necessarily need.
What is more, although clinical trials have shown mammography is effective for early breast cancer diagnosis, Wilson and colleagues note that most of these trials are decades old. “There are concerns that the benefits and harms may have changed as treatments improved and screening was applied in general practice,” they add.
For their study, the team set out to assess the link between rates of mammography for breast cancer detection and breast cancer incidence, tumor size and death rates from the disease.
They analyzed data from the Surveillance, Epidemiology and End Results (SEER) cancer registries, involving more than 16 million women aged 40 and older from 547 counties in the US.
Breast cancer was diagnosed in 53,207 of these women during the 12-month period, and these women were followed-up over the next 10 years.
The rate of breast cancer screening was assessed in each county, as determined by the percentage of women who underwent a mammogram in the previous 2 years.
Overall breast cancer incidence in the year 2000 was calculated for each county, as was the rate of breast cancer deaths during the 10-year follow-up. The team age-adjusted this data and applied it to the US population.
The results of the analysis revealed a 10% rise in breast cancer screening. This was associated with a 16% increase in breast cancer diagnosis. However, no reduction was found in the rate of breast cancer deaths.
