Single cell characterization of uterine carcinosarcoma and analysis of transcriptomic shifts in tumor-associated macrophages in metastatic and chemotherapy-treated tumors.

e17615 Background: Uterine carcinosarcoma (UCS) is a rare gynecologic malignancy that has poor clinical outcomes and few targeted therapies. This aggressive variant of endometrial carcinoma has a uniquely biphasic appearance and morphology of metastases from these tumors can be carcinoma, sarcoma, or carcinosarcoma. The tumor immune microenvironment (TIME) plays a crucial role in the behavior of cancers. Recent advances in single cell spatial transcriptomics allow for greater insight into the TIME of these aggressive tumors. Methods: Ten samples from four patients with multiple matched longitudinal samples underwent single-cell spatial transcriptomic (scST) profiling (Nanostring CosMx 6k). Standard segmentation and QC filters were applied. Cell typing was performed with confirmation by expert pathologist annotation of tissue regions. Normalized gene expression was compared within the clusters based on clinicopathologic characteristics. Results: scST profiling of 80,843 high-quality cells revealed 38 distinct clusters (11 carcinoma, 12 sarcoma, 9 immune, 7 benign mesenchymal). Tumor clusters were largely patient-specific with tumors demonstrating diverse transcriptional heterogeneity while metastatic tumors were composed of several less diverse clones. While immune cell clusters represented cells from all patients, there was significant patient and sample heterogeneity in the proportions of immune cell subsets observed. Macrophages were the most abundant immune cell type in all samples, plasma cells were common in one patient's samples, and rare T cells were found only in specific cellular niches. Transcriptomic features of intra-tumoral macrophages were assessed based on site (primary versus distant metastasis) and temporal (naïve versus treated with chemotherapy) groupings. Compared to tumor associated macrophages (TAM) in primary tumors, TAMs in distant metastases were more likely to have M2-like features with higher expression of CXCL2, CD163, CD209, and CD44 (P<0.005). TAMs residing in chemotherapy-treated tumors had higher expression of IGF2, CXCL2, CXCL1, CD163, CD209, CXCL16, CD24 , CD44, CD93 (P<0.005). Upregulation of pro-angiogenic pathways (i.e. VEGFA ) was common in both distant metastases and post-chemotherapy UCS TAMs. Conclusions: Uterine carcinosarcoma is a highly heterogeneous tumor both with respect to tumor cell and immune microenvironment features. This work highlights transcriptomic characteristics in macrophages in the UCS microenvironment. Notably, macrophages in distant metastases and in patients with prior chemotherapy were found to have more M2 TAM-like macrophages than primary untreated tumors. These results provide rationale for both TAM-based immunotherapy and anti-angiogenic approaches in UCS.