Abstract 2704: Ductal carcinoma in situ of the breast: Immune cell subset composition according to subtype
Authors: Agahozo Marie Colombe , Bockstal Mieke R. van , Groenendijk Floris H. , Bosch Thierry P. van den , Westenend Pieter J. , Deurzen Carolien H. van 
Published: August 2019

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 H&E stained sections of excision specimens from 473 patients with DCIS. These cases were subtyped based on ER, PR and HER2. Patients were categorized as TIL-high or TIL-low, whereby TIL-high was defined as high TILs density (&gt;50% of the DCIS-associated stroma occupied by TILs) with a patchy or diffuse distribution. The DCIS-associated immune cells of TIL-high cases were immunostained on consecutive whole slides with CD4 (T-helper cells), CD8 (cytotoxic T-cells), CD20 (B-cells), CD68 (macrophages), FOXP3 (regulatory T-cells), PD-L1 (immune checkpoint ligand, clones SP142 and SP263). The percentage of CD4+, CD8+, CD20+ and CD68+ immune subsets was assessed relatively to one another, with a combined score of 100%. The percentage of FOXP3+ and PD-L1+ immune cells was determined as a proportion of all immune cells. PD-L1+ DCIS cells were scored using the histo-score (H-score). The immune cell composition according to DCIS subtypes was analyzed using a Kruskal Wallis or Mann-Whitney U test.

Results: DCIS was subtyped as ER+PR+/-HER2- (n=225), ER+PR+/-HER2+ (n=80), ER-PR-HER2+ (n=85), triple negative (TN; 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&lt;0.0001). There was no statistical difference in the immune cell composition according to DCIS subtypes. However, individual DCIS subtype comparison showed that the ER+PR+/-HER2+ subtype was associated with a significantly higher proportion of CD8+ T-cells compared to the TN subtype (P=0.047). The ER-PR-HER2+ subtype was associated with a higher proportion of CD4+ T cells compared to the TN subtype, though significance was not reached (P=0.061). PD-L1 expression by both clones was low (range: 0-10% of immune cells, H-score 0-54 of DCIS cells). However, the mean value of PD-L1 SP263 was higher compared to PD-L1 SP142, for both TILs and tumor cells (P&lt;0.0001).

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.