Abstract 2875: Evidence of immunosuppression in patients with breast ductal carcinoma in situ

Abstract Introduction: Ductal carcinoma in situ (DCIS) is a noninvasive precursor to invasive breast cancer. Although not all DCISlesions progress to cancer, most DCIS are treated as early breast cancer, given the uncertainty of which lesions will progress. The current increase in the incidence of DCIS has sparked interest in the immune contexture of the DCIS lesions as well as the immune status of DCIS patients, as a means to predict which DCIS lesions will progress to cancer. Studies done so far in invasive breast cancer showed that the immune system can mediate both tumor-promoting influence (via T regulatory (Treg) cells, M2 macrophages, myeloid-derived suppressor cells (MDSCs)), as well as tumor-suppressing influences (via CD8+ and CD4+ effector T cells, natural killer cells (NK), M1 macrophages, tissue-resident memory T (Trm) cells, B cell and dendritic (DCs) cells). Similar studies are still lacking in DCIS. Our aim was to start closing the gap in our understanding of the DCIS immune microenvironment, which will pave the way for novel preventative and therapeutic strategy. Methods: We analyzed by flow cytometry peripheral blood mononuclear cells (PBMCs) from newly diagnosed DCIS patients for the presence of various immune cell types expressing specific phenotypic markers of immune effectors or immune suppressors and compared them with PBMC from age-matched healthy individuals. Results: We found a statistically significant increase in the frequency of FoxP3+ regulatory T cells in DCIS PBMC compared with healthy controls. There was also a significant increase in Tim-3+CD8+ T effector memory cells (P= 0.035) and Tim-3+ CD8+ NKT cells (P = 0.033) in the PBMCs of patients with DCIS compared with healthy controls. T cells expressing other exhaustion markers, such as PD-1+ and LAG-3+ were present at very low levels in both groups. Conclusion: Our results suggest that some of the many immunosuppressive mechanisms seen in patients with invasive breast cancer, such as regulatory T cells, are already present in pre-cancer DCIS. Evidence of the beginning of immune suppression is also reflected in the increased frequency of CD4+ and CD8+ T cells expressing the exhaustion marker Tim-3. Citation Format: Sedigheh Taghinezhad-S, Amir Hossein Mohseni, Pamela L. Beatty, Leisha A. Emens, Olivera J. Finn. Evidence of immunosuppression in patients with breast ductal carcinoma in situ [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2875.