Active Monitoring versus Surgical Excision for Atypical Ductal Hyperplasia

The recently published 2-year outcomes of the comparing an operation to monitoring, with or without endocrine therapy (COMET) trial provide evidence for the noninferiority of active monitoring of ductal carcinoma in situ (DCIS), compared with excision. These findings raise questions for the management of atypical ductal hyperplasia (ADH). To assess whether active monitoring is a safe strategy in selected patients with ADH, we used observational data on women diagnosed at an academic comprehensive cancer center and emulated a target trial of surgical excision versus active monitoring. Eligibility criteria were adapted from the COMET trial: age 40 years or older, without concurrent malignancy or a history of ipsilateral breast cancer or DCIS within the prior 5 years, without breast cancer symptoms, with no mass on physical examination or imaging, and without a history of recent endocrine therapy use. We estimated the risk of ipsilateral invasive carcinoma. There were 673 women with low-risk ADH, 238 (35.4%) of whom underwent surgical excision within 6 months. The risk of ipsilateral invasive carcinoma was 2.4% [95% confidence interval (CI), 0.8–4.1%] at 2 years with surgical excision and 0.4% (95% CI, 0–0.9%) with active monitoring (difference: 2.0; 95% CI, 0.3–3.8). At 5 years, the risk was 2.4% (95% CI, 0.8–4.2%) with surgical excision and 1.8% (0.7–3.3%) with active monitoring (difference: 0.5; 95% CI, -1.6 to 2.6). All cancers diagnosed at surgical excision or during follow-up were stage I. These findings provide evidence that active monitoring is safe and does not increase the risk of invasive carcinoma compared with surgical excision in patients with low-risk ADH.