Abstract P5-12-20: Clinicopathological Correlates of Immunohistochemistry Subtypes in Ductal Carcinoma In Situ: A Retrospective Analysis

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Abstract Introduction: Ductal carcinoma in situ (DCIS), an early neoplastic lesion confined within the mammary ductal system, exhibits considerable molecular heterogeneity, reflected in distinct immunohistochemistry (IHC) subtypes such as hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status. It's well-established that while DCIS represents a non-obligate precursor to invasive breast cancer (BC), a subset of cases harbors the potential for progression to invasive disease. Understanding the intricate molecular landscape of DCIS, particularly the interplay between IHC subtypes and the propensity for invasive progression, holds paramount importance in clinical decision-making. This study aims to investigate how IHC subtypes such as ER, PR, and HER2 in DCIS correlate with the tumor's clinicopathological characteristics. Methods: We analyzed data from the Korean Breast Cancer Society registration database, focusing on patients aged 20 and older who underwent surgery for DCIS between 2000 and 2019. Patients with confirmed lymph node metastasis or distant metastasis were excluded from the analysis. Results: A total of 11,812 patients were analyzed. Among them, 7,427 (62.9%) had HR+/HER2- breast cancer (BC), 611 (5.2%) had triple-negative breast cancer (TNBC), 1,904 (16.1%) had HR-/HER2+ BC, and 1,870 (15.8%) had HR+/HER2+ BC. At the time of diagnosis, the median age was higher in HR-BC compared to HR+ BC (HR+/HER2-: 48years, HR+/HER2+: 49years, TNBC: 53years, HR-/HER2+: 53 years). Family history was more prevalent in HR+ BC (10.5%) compared to HR-BC (8%). The proportion of asymptomatic cases was higher in HR+ BC (HR+/HER2-: 39.9%, HR+/HER2+: 45.1%) compared to HR-BC (TNBC: 34.2%, HR-/HER2+: 35.5%). Among HR-BC, the percentage of cases with a palpable lump was higher (TNBC: 30.3%, HR-/HER2+: 26.3%). Bilateral BC was more common in HR+ BC (0.5%). Tumor size (median) was larger in HER2+ BC (HR+/HER2-: 1.1 cm, TNBC: 1.2 cm, HR+/HER2+: 1.5 cm, HR-/HER2+: 1.9 cm). Mastectomy was more frequent in HER2+ BC (HR+HER2+ 40.4%, HR-/HER2+: 51.6%). Regarding nuclear grade, HR+/HER2- BC had the lowest proportion of high-grade tumors (12.5%), while HR-/HER2+ BC had the highest (73.6%). Conclusion: This study reveals the diverse clinicopathological features of DCIS based on IHC subtypes, emphasizing the importance of molecular characterization in guiding clinical management decisions. Understanding these distinct profiles can enhance prognostication and facilitate tailored treatment approaches for patients with DCIS. Citation Format: Je Hyun Chin, Doo Reh Kim, Young Joo Lee, Chang Ik Yoon, Woo Chan Park, Soo Youn Bae. Clinicopathological Correlates of Immunohistochemistry Subtypes in Ductal Carcinoma In Situ: A Retrospective Analysis [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P5-12-20.

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