News outlets this week reported on recently published data from a mammography screening study from Canada that was highly critical of the benefit of screening mammography.
First, it should be noted that this is not a new study. The study was conducted in the early 1980s – three decades ago – and the recent report is merely a re-review of the data.
The results of the so-called Canadian trial, first published 22 years ago, showed no benefit for screened women and as expected, the recent re-review showed the same results. The Canadian trial results are different than other randomized clinical trials, which do show benefit. When nine randomized clinical trials are combined together, including the Canadian trial, screening mammography has been shown to significantly decrease breast cancer mortality for women age 39 and older.
While the Canadian trial has proponents, there were substantial issues related to mammography performance in the trial that are not resolved by re-review. Unlike most screening trials, two-thirds of screened tumors were palpable at time of detection – this means the lump could be felt on physical exam. In typical screening mammogram programs, only 15% of tumors are palpable. In addition, there was little difference in the size of tumors among women with cancer, whether they were screened or not.
Since these trials were completed, numerous new observational trials across the world using modern screening mammography have confirmed the benefit of screening.
Computer models that include both modern mammography and modern treatment show a 40% breast cancer mortality reduction for women who begin screening at age 40.
While experts may have different opinions regarding when to begin mammography screening and at what frequency, all major U.S. organizations, including the American Cancer Society, the National Comprehensive Cancer Network and the U.S. Preventive Services Task Force continue to recommend regular screening mammography to reduce breast cancer mortality. Breast cancer mortality rates have continued to decrease in the United States due to advances in screening and treatment over the last 20 years.
As always, women should discuss with their provider specific breast health questions they may have.
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