Atypical Lobular Hyperplasia and Classic Lobular Carcinoma In Situ Can Be Safely Managed Without Surgical Excision.

BACKGROUND Based on modern series demonstrating low upgrade rates for pure lobular neoplasia (LN) diagnosed on core needle biopsy (CNB), our institution no longer recommends routine excision, provided imaging is concordant. This study describes outcomes in patients managed without surgical excision. METHODS From an institutional database, we identified all patients with a diagnosis of pure atypical lobular hyperplasia and/or classic lobular carcinoma in situ on CNB managed without surgical excision (i.e., conservative management) from 2015 to 2019. The primary outcome of interest was failure of conservative management, defined as development of ipsilateral same-quadrant ductal carcinoma in situ or invasive breast cancer within 2 years of CNB, or need for ipsilateral same-quadrant excisional biopsy. We also evaluated rates of ipsilateral same-quadrant CNB during follow-up. RESULTS Among 96 pure LN lesions on CNB since 2015, 80 (83%) were managed without surgical excision. Median follow-up was 27 months (IQR: 16-28), with only 2 (2%) patients lost to follow-up. No patients developed an ipsilateral, same-quadrant breast cancer. The 3-year risk of conservative management failure was 6.2% (95% CI 2.3-15.7%). All failures were a result of need for excisional biopsy due to progressive imaging abnormalities at the initial CNB site, with benign final pathology. The 3-year risk of ipsilateral same-quadrant CNB was 9.2% (95% CI 3.8-21.5%). CONCLUSION Non-surgical management of pure LN is safe, and the likelihood of requiring subsequent surgical excision or repeat CNB during follow-up is low. These data provide reassurance that routine excision of pure LN in the setting of radiologic-pathologic concordance is not required.