Clinical Outcomes and Chemoprevention in High-Risk Breast Lesions: A Comparison of Atypical Ductal Hyperplasia and Lobular Carcinoma In Situ.

BACKGROUND: Although atypical ductal hyperplasia (ADH) and lobular carcinoma in situ (LCIS) are both high-risk breast lesions, their management differs in clinical practice. We compared subsequent breast cancer outcomes between the 2 groups. METHODS: We retrospectively reviewed patients with surgically excised ADH or LCIS treated between January 2008 and December 2025. Patients with concurrent breast cancer were excluded. ADH cases upgraded to ductal carcinoma in situ (DCIS) or invasive carcinoma at excision were analyzed separately and excluded from the primary analysis. The primary endpoint was subsequent breast cancer-free survival. RESULTS: A total of 117 patients with ADH and 45 patients with LCIS were included. Four ADH cases were upgraded to DCIS and excluded from the primary analysis. No patient with pure ADH received chemoprevention, whereas chemoprevention was administered to 35 of 45 patients with LCIS (77.8%). Subsequent breast cancer developed in 14 of 113 patients (12.4%) with pure ADH and in 2 of 45 patients (4.4%) with LCIS. Subsequent breast cancer-free survival was significantly lower in the ADH cohort than in the LCIS cohort (log-rank P = .036). Among 13 evaluable subsequent breast cancers after ADH, 11 (84.6%) were hormone receptor-positive, and 6 of 14 events (42.9%) occurred more than 5 years after surgery. CONCLUSION: Despite less intensive management, patients with ADH experienced a greater burden of subsequent breast cancer than those with LCIS. These findings support recognizing ADH as a high-risk lesion and suggest that selected patients may benefit from prolonged surveillance and chemoprevention following surgical excision.