Upgrade to malignancy after excision of MRI-only B3 breast lesions: should the size and histological type of the lesion be considered for therapeutic management?

OBJECTIVES: To determine the rate of malignancy upgrade in MRI-only B3 lesions and to identify clinical, imaging, and histological features that can predict upgrade. MATERIALS AND METHODS: This retrospective single-center study included MRI-only lesions diagnosed as B3 after MRI-guided vacuum-assisted biopsy and excised between January 2007 and March 2023. We calculated upgrade rates for the entire series and for subgroups based on possible risk factors. To analyze variables considered risk factors for upgrade, we used logistic regression, calculating odds ratios (OR) and their 95% confidence intervals (CI). RESULTS: Of 592 lesions biopsied, 89 (15.03%) were classified as B3. After excluding 30 lesions because excisional specimen results were unavailable, we analyzed 59 lesions in 51 patients. Biopsy classified 15 (25.4%) lesions as pure atypical ductal hyperplasia (ADH), 27 (45.8%) as pure flat epithelial atypia (FEA), 12 (20.3%) as mixed lesions, and 5 (8.5%) as lobular neoplasia. A total of 7 (11.9%) lesions were upgraded to malignancy (71.4% to ductal carcinoma in situ, 14.3% to invasive ductal carcinoma, and 4.3% to invasive lobular carcinoma). Although histological type was not associated with upgrade to malignancy (p = 0.47), 20% of pure ADH and only 3.7% of pure FEA lesions were upgraded. Larger lesion size on MRI was associated with upgrade [6.25% of lesions ≤ 20 mm vs. 36.4% of those > 20 mm, p = 0.02; OR 8.57 (95% CI: 1.57‒46.71) p = 0.01]. CONCLUSION: Lesion size may predict upgrade in MRI-only B3 lesions independent of histological type; imaging follow-up may suffice for FEA lesions measuring < 20 mm. CRITICAL RELEVANCE STATEMENT: Considering lesion size and histological type could help define the management of MRI-only lesions classified as B3 after MRI-guided vacuum-assisted biopsy. KEY POINTS: The management of MRI-only B3 lesions has yet to be established. Lesion size is a relevant factor to consider when deciding clinical management in MRI-only B3 lesions. Conservative management appears to be safe in selected flat epithelial atypia lesions (< 20 mm).