160PCD163 EXPRESSION IN CANCER CELLS IS CAUSED BY CELL FUSION AND CANNOT BE EXPLAINED BY PARACRINE CELLULAR INTERACTION- AN IN VITRO STUDY WITH MCF-7 CELLS AND HUMAN M2-MACROPHAGES

ABSTRACT Aim: It is suggested that fusion between tumor associated macrophages and cancer cells might contribute to cancer progression, even though the extent of this phenomenon in cancer remains to be explored. Cell fusion is a normal biological process that occurs in placenta and tissue regeneration. In cancer, it is proposed to result in hybrids with increased metastatic ability and phenotypic properties from both maternal cells. The macrophage-specific antigen CD163 is expressed by tumor cells in breast cancer (BRC), an observation that is not clearly defined but proposed to be due to cell fusion. In this study we investigate cellular mechanisms that might explain CD163 expression in BRC. Methods: Monocytes (harvested from male blood donors, differentiated to M2 macrophages) were co-cultured with GFP expressing MCF-7 BRC cell line to generate MCF-7/macrophage hybrids by spontaneous cell fusion. MCF-7 cells were also cultured with M2-macrophages in transwell chamber system (TCS) allowing paracrine interaction but physical separation to prevent cell fusion. The hybrids were isolated by fluorescence-activated cell sorting based on GFP and CD163 co-expression. Hybrids were confirmed by immunofluorescence microscopy, flow cytometry, and XY-STR analysis. CD163 expression in BRC from 127 patients was examined in relation to clinical data. Results: The hybrids showed phenotypic and genotypic traits from both maternal cells; a result which could not be achieved by co-culture of these cells in TCS, indicating that CD163 expression in MCF-7 cells cannot be induced by paracrine cellular interaction. The frequency of in vitro produced hybrids was 2–5% of the total amount of macrophages. CD163 was expressed in 48% of BRC tumors and associated with shorter survival. CD163 positive cancer cells in tumor sections grew in clonal collection and a cutoff point >25% of positive cancer cells was significantly correlated to disease free and overall survival. Conclusions: Macrophage traits in BRC cells are caused by cancer cell-macrophage fusion and cannot be explained by paracrine interaction. Cell fusion might contribute to heterogeneity and clonality in BRC. These data provide new insights into the role of cell fusion in breast cancer and contributes to the development of clinical markers to identify cell fusion. Disclosure: All authors have declared no conflicts of interest.