Abstract PD9-08: Prevalence of lobular carcinoma in situ in surgical specimens of invasive breast cancer

Abstract Background: Lobular carcinoma in situ (LCIS) is a noninvasive lesion associated with a 7- to 11-fold increased risk of developing invasive breast cancer. Its incidence in biopsy specimens ranges from 0.5% to 3.6%, typically found incidentally during evaluation for another abnormality. LCIS has been reported in 5% of patients diagnosed with stage I or II invasive breast cancer and is present in approximately 50% of invasive lobular carcinoma (ILC) cases and 2% of invasive ductal carcinoma (IDC) cases. However, no recent studies have evaluated the prevalence of LCIS among patients with invasive breast cancer or its association with cancer subtypes, demographic factors, and clinicopathological features. Methods: This retrospective study included all newly diagnosed, non-metastatic breast cancer patients who underwent surgical resection at Maimonides Medical Center in 2023. The majority of pathology diagnoses were rendered by a single breast pathologist. Collected data included patient demographics, hormone receptor status, presence of multifocal disease, LCIS, and other high-risk pathological features. Fisher’s exact test was used to assess differences between LCIS-positive and LCIS-negative groups. Results: A total of 152 patients were included (150 female, 2 male). The ethnic distribution was 38.2% Caucasian, 26.3% Asian, 31.6% African American, and 3.3% Hispanic. There were 140 cases of IDC and 13 cases of ILC. The overall prevalence of LCIS in surgical specimens was 26.97% (41/152). Among LCIS-positive cases, 73% were associated with IDC and 29% with ILC. LCIS was present in 12 of 13 ILC cases (92.3%) and in 30 of 140 IDC cases (21.4%). Atypical ductal hyperplasia (ADH) or atypical lobular hyperplasia (ALH) was identified in 46.3% of LCIS-positive cases and 26% of LCIS-negative cases. The LCIS detection rate in biopsy specimens was 30.3% (46/152). LCIS was more frequently associated with estrogen receptor (ER)-positive disease (92.7%) compared to the LCIS-negative group (74%). However, 3 patients (7.3%) in the LCIS-positive group had triple-negative disease, and 8 patients (19.5%) had ER-positive, human epidermal growth factor receptor 2 (HER2)-positive tumors. Multifocal disease was also more common among LCIS-positive cases (27% vs. 9%). Conclusions: The prevalence of LCIS in invasive breast cancer surgical specimens was 26.97%, and the detection rate in biopsy specimens was 30.3%. LCIS was found in both IDC (21.4%) and ILC (92.3%) cases and was predominantly associated with ER-positive tumors (92.7%), although a minority of triple-negative cases were observed. These findings suggest a higher LCIS prevalence in both biopsy and surgical specimens than previously reported, raising questions about the potential biological significance of LCIS in breast cancer development. The presence of LCIS in ER-negative disease prompts consideration of whether endocrine-based chemoprevention should be offered to reduce the risk of future ER-positive malignancies. Citation Format: A. Zatsepina, F. Mohsin, P. Yang, L. Zhao, M. Silver, A. Corben, Y. Xu. Prevalence of lobular carcinoma in situ in surgical specimens of invasive breast cancer abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PD9-08.