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1833. Utility and Outcomes of Pre-Operative Screening Breast MRI for Planned Bilateral Prophylactic Mastectomy
Authors * Denotes Presenting Author
  1. Andrew Taliaferro *; University of California, San Francisco
  2. Elissa Price; University of California, San Francisco
  3. Jessica Hayward; University of California, San Francisco
  4. Jill Fay; Sage Women's Imaging and Specialty Ultrasound; University of California, San Francisco
  5. Rita Freimanis; University of California, San Francisco
  6. Bonnie Joe; University of California, San Francisco
  7. Amie Lee; University of California, San Francisco
Objective:
To evaluate the utility and outcomes of breast MRI performed for the indication of planned bilateral prophylactic mastectomy, including the influence on surgical management.

Materials and Methods:
An IRB-approved retrospective database review identified breast MRI exams performed at an academic center from 2000 to 2020 with the imaging indication of planned bilateral prophylactic mastectomy. Examinations were excluded if there was no BI-RADS assessment, if they were repeat MRI performed for the same indication, or if the patient had a known breast cancer at the time of imaging. Patient risk factors and prospectively reported imaging findings, breast composition, background parenchymal enhancement, and BI-RADS assessments were collected from electronic medical records. BI-RADS 1 and 2 were considered negative exams and BI-RADS 3, 4, and 5 were considered positive exams. Pathology from percutaneous biopsies and prophylactic mastectomies were recorded. In those who ultimately did not undergo mastectomy, benignity was presumed with at least 2 years of follow-up without a malignant diagnosis. Statistical analysis was performed using R (R Core Team, 2017, Vienna, Austria).

Results:
Sixty patients comprised the final cohort. Mean age was 43 years (range 23-66). The majority (44/60; 73%) had a known hereditary gene mutation and most (41/60; 68%) were baseline MRIs. Thirty-seven patients (62%) had a negative MRI and 23 patients (38.3%) had a positive MRI. Fourteen patients with a positive MRI (14/23; 60.9%) underwent percutaneous biopsy, yielding one malignancy (1/14; 7%). All 23 patients with a positive MRI underwent bilateral mastectomy, with surgery yielding an additional 2 malignancies. Malignant cases included 2 high nuclear grade DCIS and 1 invasive lobular carcinoma. The case of invasive carcinoma underwent sentinel lymph node sampling at the time of mastectomy and demonstrated nodal metastasis. Of the 37 patients with negative MRIs, 31 (83.8%) underwent prophylactic mastectomy (none demonstrating malignancy) and the remainder had long-term follow-up without malignancy. The proportion of patients who had prophylactic mastectomy did not significantly differ with age (p = 0.30), breast density (p = 1), background parenchymal enhancement (p = 0.80), genetic mutation status (p = 0.65), personal history of breast malignancy (p = 1), or the presence of multiple risk factors (p = 0.58). While not reaching statistical significance, more patients with positive MRI went on to mastectomy (p = 0.07). Overall, breast MRIs performed for planned prophylactic mastectomy demonstrated a 5% cancer detection rate, 100% sensitivity, 65% specificity, 13% positive predictive value, and 100% negative predictive value.

Conclusion:
Breast MRI performed for the indication of planned bilateral prophylactic mastectomy is highly sensitive for detecting malignancy, and may help determine the need for sentinel lymph node sampling. Larger studies are needed to establish consensus guidelines on pre-operative breast MRI prior to prophylactic bilateral mastectomy.