Abstract 7581: Loss of the duffy antigen receptor for chemokines (DARC/ACKR1) expression in ductal carcinoma in situ is associated with immune dysregulation and progression to invasive ductal carcinoma.

Abstract Ductal carcinoma in situ (DCIS) is a non-invasive precursor of breast cancer, characterized by malignant epithelial proliferation confined within the ducts. DCIS accounts for 20-25% of all breast cancer cases. Majority of DCIS lesions are treated with highly invasive surgeries and cytotoxic radiotherapy. Left untreated, 25-60% of DCIS lesions progress to invasive ductal carcinoma (IDC). Discerning which DCIS lesions will progress to IDC, to circumvent over- or under- treatment, remains a major clinical challenge. Accumulating evidence suggests that immune dysregulation within the tumor microenvironment (TME) plays a pivotal role in DCIS progression. Altered immune composition—reduced antigen presentation, T cell activation, and immune surveillance—can create a permissive environment that supports tumor growth and invasion. The Duffy Antigen Receptor for Chemokines (DARC/ACKR1), a decoy chemokine receptor expressed on erythrocytes, binds and sequesters pro-inflammatory chemokines for lysosomal degradation to maintain tissue immune homeostasis. Thus, ACKR1 regulates TME immune cell infiltration and the immune response. Loss of ACKR1 expression may disrupt chemokine gradients and impair immune cell recruitment to the TME, contributing to tumor immune evasion and progression. We hypothesize that ACKR1 influences DCIS progression by modulating immune cell composition and activation within the breast TME. We analyzed the influence of ACKR1 on the tumor immune response and DCIS TME in RNA-seq data derived from breast cancer patients in multiple independent publicly-available gene-expression datasets (GEO, Oncohuman, METABRIC) via the OmicSoft platform. We observed significant downregulation of ACKR1 expression from DCIS to IDC lesions in both the Oncohuman and METABRIC datasets, and this loss correlated with loss of E-cadherin expression in DCIS lesions. GEO analysis uncovered significant differences in a chemokine signaling network and cytokine expression profiles between ACKR1-low and ACKR1-high DCIS cases. CIBERSORT immune cell deconvolution revealed that relative to ACKR1-high lesions, ACKR1-low lesions exhibit significantly reduced proportions of naïve B cells, activated dendritic cells, CD4+ memory-activated T cells, and T follicular helper cells in DCIS. Our findings support the role of ACKR1 in shaping immune signaling within the DCIS TME by demonstrating distinct immune response profiles based on ACKR1 status. Our work suggests that loss of ACKR1 expression in DCIS supports an “immune-cold” TME, further highlighting its role as a suppressor of tumor invasion and potential biomarker of disease progression. Thus, ACKR1 may improve clinical decision making and DCIS patient management by providing insight into patient immune response profiles and predisposition for progression. Citation Format: Dana Franklin, Ni-Chun Tsai, Hyejin Cho, Yate-Ching Yuan, Yuqi Zhao, Padmashree Rida, Nikita Jinna. Loss of the duffy antigen receptor for chemokines (DARC/ACKR1) expression in ductal carcinoma in situ is associated with immune dysregulation and progression to invasive ductal carcinoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7581.