Abstract 3788: EpCAM+ DCCs isolated from the bone marrow of breast cancer patients display high stemness and potency scores

Abstract Metastatic dissemination of cancer cells from primary to distant sites often occurs early and it has been shown that their detection is linked to poor outcomes. Eradication of disseminated cancer cells (DCC) has therefore become the primary goal of adjuvant therapies. Since the phenotype of DCC is largely unknown, we set out to search, isolate, and molecularly characterize these candidate metastasis founder cells from bone marrow of breast cancer patients, years before manifestation of metastasis. We screened more than 200 bone marrow samples of breast cancer patients with no evident metastasis (UICC stage M0) for EpCAM-positive cells. EpCAM positive cells in the bone marrow of healthy donors were used as a negative control. In addition, we isolated DCC from breast cancer patients with manifest metastasis (UICC stage M1). We then performed single cell RNA sequencing after whole transcriptome amplification of the collected DCC and the healthy donor (HD) control cells. To confirm the malignant origin of picked DCCs, we projected the transcriptome data into the bone marrow atlas, inferred copy number alterations, and searched for mutations shared with the matched primary tumor. EpCAM-positive cells from control patients mostly comprised plasma cells. In contrast, DCCs derived from M0-stage breast cancer patient formed a unique, non-overlapping cluster in the bone marrow atlas. UMAP-clustering placed M1-stage DCC clearly separate from M0 stage DCC. Among the collected M0-stage DCCs, we identified at least three separate subclusters. Strikingly, M0-stage DCC displayed much higher stemness and potency scores than M1-stage DCCs, reminiscent of embryonic cells. DCCs, identified by EpCAM, display very high transcriptional stemness scores when isolated before metastatic manifestation. Upon expansion and proliferation, stemness scores are reduced indicating epithelial re-differentiation. The embryonic phenotype of M0-stage DCCs may reflect an early adaptive mechanism that enables DCC to survive in an ectopic environment and may impact on the metastatic potential of the DCC. Citation Format: Elia Raya, Huiqin Koerkel-Qu, Laura Rudhart, Lisa-Marie Köhler, Anna Damboeck, Christoph Irlbeck, Catherine Botteron, Melanie Werner-Klein, Stephan Seitz, Christoph Klein. EpCAM+ DCCs isolated from the bone marrow of breast cancer patients display high stemness and potency scores abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 3788.