Multiple Bilateral Circumscribed Masses at Screening Breast Ultrasound: Outcomes of New or Enlarging Masses at Follow-Up.

Abstract

BACKGROUND. Breast screening ultrasound (US) has limited specificity but is increasingly performed because of widening state and federal legislation regarding breast density. There is a need for evidence-based management guidelines. OBJECTIVE. The purpose of this study was to assess outcomes of new or enlarging oval circumscribed parallel masses in the setting of multiple bilateral circumscribed masses (MBCM) at sequential rounds of US screening. METHODS. In this retrospective study of women found to have MBCM on screening breast US without mammography abnormalities, longitudinal review was performed to identify development of any new or enlarging or changing masses. Outcomes were recorded using biopsy results or minimum of 12 months of follow-up as reference standards. Lesion characteristics, BI-RADS classification, breast density, patient age, demographics, and risk factors were reviewed. Statistical analysis included multivariable logistic regression analysis. RESULTS. There were 284 (2.4%) cases of MBCM in a total of 48,488 bilateral screening US examinations performed in 11,826 asymptomatic women between January 1, 2014, and July 31, 2019, that fit inclusion criteria. Of the 284 women (mean age, 46 years; range, 20-83 years), 150 (52.8%) subsequently developed 465 new, enlarging, and/or changing masses, 107 (23.0%) of which underwent biopsy. Of the 465 masses, 408 (87.7%) were oval circumscribed parallel masses and similar to other MBCM, and 57 (12.3%) were unique findings that were nonoval noncircumscribed masses. None of the new or enlarging oval circumscribed parallel masses were malignant. In total, the malignancy rate was 0% for women with MBCM with follow-up (median, 40.8 months; range, 12-75 months) and 0% for those that underwent biopsy (95% CI, 0-1.2%). Among women with concurrent MBCM and unique findings, four cancers were detected. Three were new irregular masses, and one previously oval mass changed in morphology to have new calcifications and an irregular border. A younger age was related to the likelihood of having enlarging masses (p < .001). CONCLUSION. In the setting of MBCM, new or enlarging oval circumscribed parallel masses are a common and benign event. Concurrent new irregular masses or previously oval masses that develop suspicious morphologic features should be carefully evaluated for malignancy. CLINICAL IMPACT. Breast radiologists who encounter new or enlarging oval circumscribed parallel masses with no suspicious morphologic change in the setting of MBCM can safely defer biopsies.