Abstract 2704: Ductal carcinoma in situ of the breast: Immune cell subset composition according to subtype

Introduction: Ductal carcinoma in situ (DCIS) of the breast includes several subtypes with a divergent biological behavior. HER2+ DCIS is often detected at the in situ stage, while ER- HER2- DCIS is relatively rare. Besides, HER2+ DCIS has a more extensive growth pattern compared to other subtypes. Data regarding the composition of DCIS-associated immune cells and their potential role in DCIS progression is limited. We studied DCIS-associated immune response by characterizing immune cell subsets according to DCIS subtypes. Methods: We evaluated DCIS-associated tumor infiltrating lymphocyte (TIL) density and distribution based on HE n=22) or missing (n=31). In total, 131/473 patients (27.7%) were considered as TIL-high and the percentage of TIL-high cases was significantly associated with DCIS subtype (11.4% of ER+PR+/-HER2-, 38.8% of ER+PR+/-HER2+, 61.2% of ER-PR-HER2+ and 63.6% of the TN subtype, P Conclusion: High numbers of TILs are mainly observed in HER+ and TN DCIS subtypes. The ER+ HER2+ DCIS subtype attracts more CD8+ T-cells compared to the TN subtype. This suggests a more pronounced anti-tumor immunity in HER2+ DCIS, which could play a role in its biological behavior. Citation Format: Marie Colombe Agahozo, Mieke R. van Bockstal, Floris H. Groenendijk, Thierry P. van den Bosch, Pieter J. Westenend, Carolien H. van Deurzen. Ductal carcinoma in situ of the breast: Immune cell subset composition according to subtype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2704.