One year overview of the molecular breast imaging clinical practice at Mayo Clinic

2676 Objectives Molecular breast imaging (MBI) has shown utility for detection of mammographically-occult breast cancers. In two research trials conducted in women with mammographically dense breasts, the addition MBI detected an additional 8 to 9 cancers per 1000 women screened, compared to that of mammography alone [1,2]. Following implementation of MBI in our clinical practice, our objective was to review its clinical use and assess performance metrics. Methods We reviewed records from all patients who had MBI performed at our institution in the year 2015. Patients received an intravenous injection of 8 mCi Tc-99m sestamibi; bilateral cradiocaudal and mediolateral oblique projections were acquired for 10 min/view using a dual-head CZT-based gamma camera optimized for low-dose imaging. Breast radiologists interpreted MBI along with comparison mammograms where available, and assigned an assessment that parallels BI-RADS of 0 through 6, where 0, 3, 4, and 5 are considered positive and led to diagnostic workup. We recorded indications and referral patterns, and audited the recall rate, biopsy rate, and cancers detected by MBI. Results A total of 592 women underwent MBI, of which 564 (95%) were presenting for screening. The remaining 28 had MBI as part of diagnostic workup for a known lesion. MBI patients were referred from providers in the following areas: Breast Diagnostic Clinic, 234 (40%); Primary Care/General Internal Medicine, 197 (33%); Preventive Medicine, 82 (14%); OB/Gyn, 47 (8%); Family Medicine, 19 (3%); Oncology, 8 (1%); Outside referrals, 6 (1%). Mammographic breast density, assessed per ACR BI-RADS categories on mammogram performed closest to MBI, was considered dense (heterogeneously or extremely) in 544 (92%), non-dense (fatty replaced or scattered fibroglandular densities) in 48 (8%). 527 of 592 (89%) women had mammography performed within one year of MBI. Of the 564 screening patients, the primary indication for MBI was a history of mammographically dense breasts in 545 (97%) women. In the remaining 19 (3%) women, screening magnetic resonance (MR) imaging was recommended but MBI was performed instead due to MR contraindications or inability to pay for the MR exam. 72 of 564 screening patients had positive MBI findings (recall rate = 72/564 (13%)) and underwent immediate diagnostic mammography and/or targeted ultrasound. 34/72 (47%) were resolved by this workup, 14 went on to have immediate MRI, and 24 were recommended to return for MBI follow-up in 6 months. MBI findings led to biopsy in 18 screening patients (biopsy rate = 18/564 (3%)), of which 3 biopsies showed malignancy (PPV = 3/18 (17%)), including the following: 2.6-cm, grade III, invasive ductal carcinoma; 1.2 cm, grade II, invasive ductal carcinoma; and 0.9 cm, intermediate grade ductal carcinoma in situ. Most recent mammogram was negative in all 3 cases. There were no mammographically detected cancers in this cohort. Conclusions MBI was shown to detect mammographically-occult cancers in women with dense breasts, with a low recall rate and low biopsy rate relative to that reported for other modalities used in supplemental screening. [1] Rhodes et al. Radiology 2011 [2] Rhodes et al. AJR 2015