Given that we have found no evidence of reduced overall advanced contralateral breast cancer events, patients and physicians must carefully balance the risks and benefits of preoperative MRI use.
Shi-Yi Wang, MD, PhD, and colleagues
In an analysis of the Surveillance, Epidemiology, and End Results (SEER)-Medicare database reported in the Journal of Clinical Oncology, Shi-Yi Wang, MD, PhD, of Yale School of Public Health, and colleagues found that the use of preoperative magnetic resonance imaging (MRI) was associated with overdiagnosis of contralateral breast cancer among older women with breast cancer.1
The study involved data on overall, synchronous (< 6 months after primary diagnosis), and subsequent contralateral breast cancer from 38,971 women diagnosed with stage I or II breast cancer between 2004 and 2009 who were aged 67 to 94 years at the time of diagnosis and who were observed through 2011. Overall, women had a mean age of 76.4 years.
A total of 6,737 women (16.4%) had received preoperative MRI. Those who received MRI tended to be younger, white, married, have higher median income, and have fewer comorbidities. Propensity score matching was used to adjust for baseline characteristics and account for potential treatment selection bias.
Contralateral Cancer Detection Rates
In the propensity-score matched cohort, accounting for 73,489 person-years of follow-up and median follow-up of 43 and 46 months for the MRI and non-MRI groups, the MRI group had a higher rate of overall in situ plus invasive contralateral breast cancer (18.9 vs 9.2/1,000 person-years, hazard ratio [HR] = 2.01, P < .001) and a higher synchronous contralateral breast cancer detection rate (126.4 vs 42.9/1,000 person-years, HR = 2.85, P < .001) but a lower subsequent contralateral breast cancer detection rate (3.3 vs 4.5/1,000 person-years, HR = 0.68, P = .002).
Women who received MRI had a higher rate of both synchronous in situ contralateral breast cancer (47.9 vs 12.9/1,000 person-years, HR = 3.66, P < .001) and invasive contralateral breast cancer (78.6 vs 30.0/1,000 person-years, HR = 2.52, P < .001) and were more likely to have invasive contralateral breast cancers that were stage I (57.3 vs 18.9/1,000 person-years, HR = 2.92, 95% confidence interval [CI] = 2.42–3.52) and stages II to IV (18.2 vs 10.4/1,000 person-years, HR = 1.67, 95% CI = 1.25–2.22). Women who received MRI had a higher rate of subsequent in situ contralateral breast cancer (1.8 vs 1.2/1,000 person-years, HR = 1.59, P = .012) and a lower rate of subsequent invasive contralateral breast cancer (1.6 vs 3.4/1,000, HR = 0.39, P < .001).
After 5 years of follow-up, cumulative incidence of contralateral breast cancer (both in situ and invasive) was 7.2% in the MRI group vs 4.0% in the non-MRI group (P < .001), including a higher incidence of invasive contralateral breast cancer (4.3% vs 2.9%, P < .001).
Analysis of projected contralateral breast cancer events for 10,000 patients receiving MRI indicated that, after 5 years of follow-up, MRI use would be associated with an additional 377 synchronous contralateral breast cancers and 58 fewer subsequent contralateral breast cancers, with detection of an additional 192 in situ contralateral breast cancers and 120 stage I contralateral breast cancers but only an additional 6 stage II to IV contralateral breast cancers. On modeling, using total contralateral breast cancer occurrence in the MRI group as the denominator, it was estimated that 45.3% of contralateral breast cancers detected in the MRI group were overdiagnosed.
The investigators concluded: “An increased synchronous contralateral breast cancer detection rate, attributable to MRI, was not offset by a decrease of subsequent contralateral breast cancer occurrence among older women with early-stage breast cancer, suggesting that preoperative MRI in women with breast cancer may lead to overdiagnosis.”
They further noted:
We found that preoperative breast MRI use was associated with a shift in stage at diagnosis for subsequent contralateral breast cancer events—an increase of subsequent in situ contralateral breast cancer occurrence but a decrease in subsequent invasive contralateral breast cancer occurrence. However, the decrease in subsequent contralateral breast cancer events did not counteract a large net increase in synchronous contralateral breast cancer detection that was attributed to MRI use. Given that we have found no evidence of reduced overall advanced contralateral breast cancer events, patients and physicians must carefully balance the risks and benefits of preoperative MRI use. ■
Disclosure: The study was supported by Yale Comprehensive Cancer Center, California Department of Public Health, National Cancer Institute SEER Program, and Centers for Disease Control and Prevention National Program of Cancer Registries. For full disclosures of the study authors, visit jco.ascopubs.org.
1. Wang SY, Long JB, Killelea BK, et al: Preoperative breast magnetic resonance imaging and contralateral breast cancer occurrence among older women with breast cancer. J Clin Oncol 34:321-328, 2016.
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