Her2 Positive Dcis Increases Short Term Risk Of Ipsilateral Invasive Ductal Carcinoma In Breast Conserving Surgery Patients

Purpose: The impact of HER2 status in ductal carcinoma in situ (DCIS) lesions on the risk of progression to invasive ductal carcinoma (IDC) has been debated with reports of both increased and decreased risk of development of invasive breast cancer in HER2 positive patients. We aim to use a large national database to elucidate the effect of HER2 positivity on ipsilateral IDC (iIDC) development. Methods: We performed survival analyses on patient-level data using the US National Cancer Institute9s Surveillance, Epidemiology, and End Results program to identify patients diagnosed with DCIS who underwent lumpectomy and had known HER2, estrogen and progesterone receptor statuses, grade, comedonecrosis, age, tumor size, and radiation therapy (RT). Competing risks analysis was performed. Results: 1,540 patients meeting inclusion criteria were identified. Median age at diagnosis was 60 with median follow-up time of 44.5 months. 22 (1.4%) patients developed iIDC and 27 (1.8%) developed ipsilateral in situ or contralateral disease. 1,035 (67.2%) patients were HER2 negative and 417 (27.1%) were HER2 positive. The estimated cumulative incidence of iIDC at 5 years was 1.9% for all patients, 1.2% (95% CI 0.6-2.1%) for HER2 negative patients, and 4.0% (95% CI 2.9-5.4%) for HER2 positive patients. On competing risks regression, two factors were significant for iIDC: RT within 20 months (HR=0.02, p=0.0002) and HER2 positivity (HR=2.81, p=0.046). Conclusions: HER2 may serve as a prognostic factor for consideration in decision making in patients for whom it is available, and in our analysis was the only lesion-related factor to significantly relate to iIDC development. Citation Format: Thomas O9Keefe, Sarah Blair, Ava Hosseini, Olivier Harismendy, Anne Wallace. HER2 positive DCIS increases short term risk of ipsilateral invasive ductal carcinoma in breast conserving surgery patients [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6461.