We’ve heard the rally cries – “put your breast foot forward,” “feel for lumps; save your bumps”, “save second base” and “big or small, let’s save ’em all!” The reality is that in the United States this year, an estimated 268,600 new cases of invasive breast cancer will be diagnosed in women. An estimated 41,760 women will die from breast cancer this year. (1)
Magnetic resonance imaging (MRI) are the go-to for most women when trying to find cancer in the breast. MRI scans and mammogram led to fewer missed cancers – but for women with dense breasts, these tests often result in false alarms and treatments that might not have been needed, a large study found.
The results of the research – Supplemental MRI Screening for Women with Extremely Dense Breast Tissue – were presented at the Clinical Trials in Radiology session at the European Congress of Radiology 2019.
The results offer a clearer picture of the tradeoffs involved in mammograms, but do not (and cannot) answer the question: Does it save lives?
For women with dense breasts trying to decide on screening, “the dilemma remains,” Dr. Dan Longo of the New England Journal of Medicine wrote in an editorial published with the study.
“The most unexpected finding that has emerged from screening studies for breast, lung, and prostate cancer is that an imprecisely defined fraction of the cancers that are detected by screening do not progress to cause symptomatic disease or to kill the patient,” he said. “The growth fraction of tumors is continuously declining; the problem is that tumors do not stop their growth until the tumor burden has become lethal in most cases.” (2)
About half of women over 40 have dense breasts and about 10% have very dense ones. That raises their risk of developing cancer and makes it harder to spot on mammograms if they do. U.S. regulators are making rules to require that women get breast density information when they have mammograms, and many places provide it now. But what to do if you have dense breasts is unclear – it’s not known if more or different types of screening such as MRIs or ultrasounds help.
“According to current practice,” Dr. Long said, “women with extremely dense breast tissue on mammography must be informed that their breasts are dense. … Unfortunately, it is not clear to the women or their physicians what steps need to be taken as a consequence of that information.
“Follow-up ultrasonography has not been very helpful. Informally, many doctors have been sending women with dense breasts for magnetic resonance imaging, a test that is more sensitive but far less specific than mammography. But until now, it was unclear whether that additional testing had any value.”
The study involved more than 40,000 Dutch women ages 50 to 75 with very dense breasts who had normal results from a mammogram, a screening X-ray offered every two years in the Netherlands. About 8,000 of them also were offered an MRI scan, which uses powerful magnets to create detailed images, and 4,783 women agreed.
Researchers then tracked how many breast cancers were detected in each group within two years. Finding more of these “interval cancers” implies that the initial screening may have missed them.
The rate of these cancers after two years was twice as high in the group that was only offered mammograms. This suggests that adding MRIs to initial screening did catch more cancers, but they also gave a lot of false alarms – about 80 per 1,000 scans. Three quarters (74%) of women who had a biopsy after a questionable MRI turned out not to have cancer.
Without such evidence, it is difficult to surmise the value in finding more cancers, especially many early stage ones, Longo wrote. Doctors already know that some of these will never cause symptoms or become life-threatening.
“Our dilemma is that, for most tumors, we cannot tell the difference between cancers that can kill you and those that cannot,” he wrote.
- Cancer Facts & Figures 2019. https://www.cancer.org/content/dam/cancer-org/research/cancer-facts-and-statistics/annual-cancer-facts-and-figures/2019/cancer-facts-and-figures-2019.pdf
- Detecting Breast Cancer in Women with Dense Breasts. New England Journal of Medicine. https://www.nejm.org/doi/full/10.1056/NEJMe1912943