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Abstract Background Epithelial–mesenchymal transition (EMT) is linked to an immunosuppressive tumor microenvironment (TME). However, direct comparisons of the TME in paired tumor regions with and without EMT in primary tumors—essential for elucidating EMT’s impact on the TME—are still lacking. Methods Using Digital Spatial Profiler (DSP) assay and NanoString nCounter Digital Profiling, we analyzed immune-oncology-related markers in the TME of no special type (NST) and paired spindle carcinomatous (SPS) components, the later considered the EMT counterpart of the former, in nine cases of metaplastic breast carcinoma, a type of mammary carcinosarcoma. Results We identified macrophage markers as consistently and significantly enriched immune-oncology-related proteins within the TME profiles of SPS components compared to their paired NST counterparts. Additionally, we observed notable enrichment of macrophage-related signatures, M2 macrophage phenotypes, M2 macrophage-inducing cytokines, and M2 macrophage-related genes, as key distinctions in the TME profiles of SPS components relative to NST counterparts. Immunohistochemistry and multiplex immunofluorescence confirmed the presence of M2 macrophages, predominantly characterized by CD14 + /CD68 + /CD163 + phenotypes, in the SPS components. The in vivo findings were supported by in vitro analysis, which revealed that primary breast cancer cells undergoing spontaneous EMT exhibit enhanced induction of M2 macrophage polarization, with CSF1 contributing to this effect. Despite some heterogeneity, the upregulation of CSF1 and CCL2 likely contributed to the increased presence of M2 macrophages in the SPS components in MpBC cases. This EMT-driven M2 macrophage-enriched TME was also observed in sarcomatous versus carcinomatous components in nonmammary carcinosarcomas across organs, as well as in vimentin-positive versus vementin-negative triple-negative breast cancer, where vimentin expression is associated with EMT. Conclusions Given the immunosuppressive role of M2 macrophages, our findings suggest that an EMT-driven, M2 macrophage-enriched TME—a consistent phenomenon across organs—can contribute to immune suppression. This underscores the therapeutic potential of macrophage-targeting strategies and immune checkpoint inhibition in treating aggressive carcinosarcomas characterized by EMT-mediated, M2 macrophage-rich TMEs.
Lien et al. (Tue,) studied this question.