Clustered Microcysts at Breast US: Outcomes and Updates for Appropriate Management Recommendations.

Background Clustered microcysts are common, especially in perimenopausal women, and are seen in up to 6% of US examinations. However, there are limited published data on appropriate assessment and management recommendations for clustered microcysts on breast US images. Purpose To determine outcomes of lesions identified as clustered microcysts on breast US images to help guide appropriate management recommendations. Materials and Methods Lesions classified as clustered microcysts at breast US were retrospectively identified in women at two hospitals (a large tertiary care academic hospital and a National Comprehensive Cancer Network-designated comprehensive cancer center) within one metropolitan health system from 2005 through 2015. If US-guided tissue sampling was performed, results were obtained from the pathology or cytology reports. If sampling was not performed, only lesions with at least 24 months of imaging follow-up or any imaging follow-up with interval resolution or decrease in size were included in the study. Data were evaluated using standard statistics, Fisher exact tests, and Wilcoxon rank sum tests. Results A total of 189 women (median age, 52 years [interquartile range, 46-59 years]) with 196 lesions classified as clustered microcysts on US images were included in this study. During the surveillance period of at least 24 months and at tissue diagnosis, malignancy was not found in any of the 196 lesions (0%) (95% confidence interval: 0.0%, 1.9%). A total of 158 of 196 (80%) lesions were followed with imaging, and 38 of 196 (20%) lesions underwent percutaneous sampling. During the follow-up period, 28 of 158 (18%) lesions spontaneously resolved, 13 of 158 (8%) decreased in size, and one of 158 lesions (0.6%) increased at 18-month follow-up but then became stable. One hundred sixteen of 158 lesions (73%) demonstrated no change at follow-up imaging, 38 of 196 (19%) lesions underwent percutaneous sampling, and 38 of 38 (100%) revealed benign results. Conclusion No malignancies were identified in this series. These results further support the existing literature that lesions characterized as clustered microcysts demonstrate a very low risk of malignancy and can be classified as benign. Biopsy may be safely avoided. © RSNA, 2020 See also the editorial by Berg in this issue.