Multiple bilateral circumscribed masses at screening breast US: Consider annual follow-up

Purpose: To determine prospectively the prevalence and rate of malignancy of multiple bilateral (MB) circumscribed breast masses detected at screening ultrasonography (US) compared with those of other US-depicted masses. Materials and Methods: This institutional review board-approved, HIPAA-compliant prospective trial included women at elevated risk for breast cancer, who gave written informed consent to participate in a study evaluating cancer detection rates for three rounds of annual supplemental screening US at 21 international sites. After exclusions, 2662 participants and 7473 screening studies were included. Physicianperformed US studies were interpreted, with blinding to mammography results. Simple cysts were noted. Breast Imaging Reporting and Data System features of all other findings were recorded, with addition of the descriptor MB similar-appearing circumscribed masses (minimum of three total and at least one in each breast), with details of the largest such mass recorded. Rates of malignancy were determined after biopsy or mammographic and US follow- up at a minimum of 11 months. For this analysis, 490 women (1370 screenings) with prior mastectomy were excluded. Descriptive statistics and exact 95% confidence intervals (CIs) were generated. Results: Of 2172 evaluable participants (6103 screening studies; median age at study entry, 54.0 years; range, 25-91 years), 1454 had unique findings at US. One hundred thirty-five (6.2%) participants had 153 unique MB circumscribed masses, with no malignancies (0% [95% CI: 0%, 2.4%]; 95% CI: 0%, 2.9% for the 127 masses with at least 2 years of follow-up). There were 1319 (60.7%) participants with 2464 non-MB lesions, including 1038 solitary circumscribed masses with a malignancy rate of 0.8% (eight of 1038). Of 836 solitary circumscribed masses with at least 2 years of follow-up, the malignancy rate was 0.4% (three of 836; 95% CI: 0.1%, 1.0%). Of the 135 women with MB circumscribed masses, 82 (60.7%) also had a solitary lesion. Two of these 82 women (2.4%) had cancer. Conclusion: MB similar-appearing circumscribed masses seen at screening US are almost always benign, with no malignancies found among such lesions in this prospective, multicenter experience. These lesions are suitable for diagnostic follow-up in 1 year, with resumption of screening thereafter if they are stable.