Performance Measures of Magnetic Resonance Imaging Plus Mammography in the High Risk Ontario Breast Screening Program

Anna M. Chiarelli; Kristina M. Blackmore; Derek Muradali; Susan J. Done; Vicky Majpruz; Ashini Weerasinghe; Lucia Mirea; Andrea Eisen; Linda Rabeneck; Ellen Warner

Disclosures

J Natl Cancer Inst. 2020;112(2):136-144. 

In This Article

Results

The final cohort included 8782 women who underwent 20 053 MRI and mammography screening examinations with a final result (Figure 1). Women excluded (n = 521) were more likely to be age 50–69 years (34.7% vs 26.4%; P < .001) or postmenopausal (41.4% vs 36.2%; P = .03). MRIs (94.0%) were usually within 30 days of the mammogram, and 85.5% of screening episodes were within 15 months (mean = 13.5 months).

The majority of screened women (73.6%) were age 30–49 years at their initial screening examination, had at least two screening rounds (68.3%), were premenopausal (62.2%), and had a family history and estimated personal lifetime breast cancer risk of 25% or higher (72.6%) (Table 1).

The biopsy rate was highest for MRI plus mammography (7.1%) (Table 2). There were 280 screen-detected breast cancers (cancer detection rate: 14.0 per 1000, 95% CI = 12.4 to 15.7). The cancer detection rate for MRI plus mammography was higher on the initial screens (17.1 per 1000, 95% CI = 14.6 to 20.0) compared with rescreens (11.5 per 1000, 95% CI = 9.7 to 13.7). By age, the detection rate for MRI plus mammography was greater among women age 50–69 years (19.3 per 1000, 95% CI = 16.2 to 23.0). By risk group, the detection rate for MRI plus mammography was highest among known mutation carriers (26.8 per 1000, 95% CI = 22.6 to 31.8).

Sensitivity was 96.0% (95% CI = 92.2% to 98.0%) for MRI plus mammography, and as single modalities 40.8% (95% CI = 29.3% to 53.5%) for mammography and 90.8% (95% CI = 84.7% to 94.7%) for MRI (Table 3). Among age groups, a statistically significant increase in sensitivity for the combination compared with MRI alone was observed for women age 40–49 years (92.4%, 95% CI = 85.1% to 96.3% vs 85.9%, 95% CI = 77.3% to 91.6%, P = .01) and age 50–69 years (96.3%, 95% CI = 90.6% to 98.6% vs 90.9%, 95% CI = 83.6% to 95.1%, P = .02). Of the screen-detected cancers in mutation carriers, MRI missed one of 26 cancers in those age 30–39 years and one of 32 cancers in those age 40–49 years. However, in mutation carriers age 50–69 years, the combination found five (9.2%) more breast cancers than MRI alone (92.7%, 95% CI = 82.1% to 97.2% vs 83.5%, 95% CI = 71.0% to 91.3%, P = .02). Of the screen-detected cancers in women with a family history and lifetime risk of 25% or higher, MRI missed two of 23 cancers in those age 30–39 years, five of 45 cancers in those age 40–49 years, and one of 49 cancers in those age 50–69 years.

The combination statistically significantly reduced specificity to 81.0% (95% CI = 78.7% to 83.1%) compared with 91.8% (95% CI = 90.6% to 92.8%) for mammography alone and 87.3% (95% CI = 85.6% to 88.9%) for MRI alone (Table 4). By age, the smallest decrease in specificity from adding mammography to MRI compared with MRI alone was among women age 50–69 years (84.2%, 95% CI = 83.1% to 85.2% vs 90.0%, 95% CI = 89.2% to 90.9%, P < .001). When stratified by risk and age group, the largest decrease in specificity between the combination and MRI was among mutation carriers age 30–39 years (78.0%, 95% CI = 74.7% to 80.9% vs 86.2%, 95% CI = 83.5% to 88.5%, P < .001).

Of the 57 screen-detected DCIS cases, mammography detected only five (8.8%) missed by MRI, whereas MRI detected 36 (63.1%) missed by mammography (Table 5). Of the 28 low-grade invasive cancers, mammography detected only two (7.1%) missed by MRI compared with 22 (78.6%) detected by MRI. MRI-detected invasive cancers were more likely to be stage I (88.6%) and lymph node negative (96.2%) compared with cancers seen on both modalities. The majority of the 12 interval cancers were invasive (66.7%), and of these, a higher proportion were histologic grade III (75%), stage I (71.4%), and none was diagnosed in mutation carriers age 30 to 39 years (Table 6).

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