• Surgical excision of all microscopic subclinical disease is not necessary to achieve good long-term outcomes.
In National Surgical Adjuvant Breast and Bowel Project studies from the 1990s, in the era before the use of aromatase inhibitors or HER-2 blockade, the 10-year incidence of ipsilateral breast tumor recurrence ranged from 3.5% to 6.5% in the breast cancer population at large.
In addition, the incidence of contralateral breast cancers has been declining at a rate of approximately 3% per year, thanks to the use of adjuvant systemic therapies.
We have known since the 1960s, thanks to our colleagues in pathology, that somewhere between 30% and 60% of breast cancers that appear to be localized have microscopic subclinical disease which is treated with breast irradiation. More recently, we have recognized that we can leave behind cancer in the axilla in anywhere from 13% to 27% of patients who are not receiving direct axillary radiation, and see failure rates of 1% or less.
In the context, then, of our current understanding of breast cancer biology, what outcomes could MRI be expected to improve, since the purpose of a test is to improve patient outcomes?
We know that MRI will not improve survival, because 30 years ago randomized trials showed us that survival was equal between breast conservation and mastectomy.
MRI has no apparent effect on reducing local recurrences either, as shown in an analysis of data on 3,180 patients published in 2014 (J Clin Oncol. 2014;32:292).
Regarding contralateral breast cancer, a 2007 study (N Engl J Med. 2007;356:1295-303) showed that among 969 women, MRI found unsuspected cancer in the contralateral breast within 1 year of diagnosis in 3.1%, a finding used to support the argument that all women with breast cancer should have an MRI. But a second study using Surveillance, Epidemiology and End Results (SEER) data on 339,790 women with 2.5 million person-years of follow-up found that the 10-year rate of contralateral cancers was 2%-3% of women with estrogen-receptor–positive tumors, and in 5%-6% of those with estrogen-receptor–negative tumors, strongly suggesting that MRI leads to detection and treatment of disease that would never become clinically evident.
Finally, I would point to evidence that MRI does not improve short-term surgical outcomes, as shown in a meta-analysis my colleagues and I conducted of two randomized controlled trials and seven cohort studies, involving a total of 3,112 patients (Ann Surg. 2013;257:249-55).
We found that after adjustment for age, having an MRI was associated with a three-fold greater chance of having a mastectomy, and MRI did not significantly reduce either the need for re-excision or unexpected conversion to mastectomy. We also performed a subanalysis of infiltrating lobular cancers, and found that there was no statistically significant benefit for MRI in these patients.
The overall rate of mastectomy was 25.5% among patients who had an MRI, vs. 18.2% for those who did not.
So to summarize: MRI finds two to three times more cancer than observed rates of local recurrence, leading to unnecessary mastectomies and does not improve short-term surgical outcomes, and there is no evidence indicating that MRI decreases local recurrence.
Monica Morrow, MD, FACS, is chief of the breast service in the department of surgery and holds the Anne Burnett Windfohr Chair of Clinical Oncology at Memorial Sloan Kettering Cancer Center in New York.