Downstream imaging following abnormal molecular breast imaging, lessons learned and suggestions for success

Objectives: Molecular breast imaging (MBI) is a supplemental screening modality that assists in detection of breast cancer. Objectives were to investigate how abnormal MBI findings were further evaluated on subsequent imaging studies and assess outcomes.

Methods: Retrospective single-institution review included patients who underwent supplemental screening MBI between October 2018 and October 2021, utilizing 300 MBq (8 mCi) ^99mTc-sestamibi as radiotracer. Patients with abnormal MBI were assessed for subsequent imaging, biopsies, or surgeries performed. Outcome metrics included recall rate, cancer detection rate, and positive predictive values for recall (PPV1) and biopsy (PPV3); 95% confidence intervals calculated via Wilson score interval. All tests were two-sided; p < 0.05 considered statistically significant.

Results: Total of 716 MBI exams performed, 93 of which were read as abnormal with ultimate detection of 11 malignancies. Recall rate was 13.0%, cancer detection rate was 15.4/1000 (invasive: 11.2/1000), PPV1 was 11.8%, and PPV3 was 27.5%. Of 11 malignancies, 7 (63.6%) were not visible on concurrent or most recent mammogram. Initial subsequent imaging study detected a correlate for mass uptake in 20/22 (90.9%) cases compared to 42/70 (60.0%) for nonmass uptake (p < 0.007), with correlates for nonmass uptake seen on ultrasound or mammogram in only 5/19 (26.3%). MRI was utilized in 63 (8.8%) cases overall.

Conclusion: Screening MBI afforded a high cancer detection rate, yet lower detection of nonmass uptake on subsequent ultrasound/mammography resulted in increased usage of MRI compared to prior reports. As utilization of MBI increases, more reported experiences are needed to establish best practices and understand effects of implementation.