Abstract
BACKGROUND: Extrahepatic cholangiocarcinoma (eCCA) is a rare but refractory cancer with dense desmoplasia. Prognosis-associated stromal cells in eCCA remain poorly characterized. Here, we profiled the tumor cellular composition and identified prognosis-related stromal signatures by single-cell RNA sequencing (scRNA-seq) in eCCA. ECCA patients were further stratified into different categories based on identified stromal signatures. METHODS: Using scRNA-seq, we profiled the transcriptomes of 37,498 individual cells from eight eCCA biopsies, including five tumor tissues and three paired adjacent normal tissues. Bulk RNA sequencing (bRNA-seq) was also performed on 43 eCCA tumor tissues. Stromal cell composition and heterogeneity were examined through differential gene expression and gene set enrichment analyses. By assessing the expression levels of marker genes in bRNA-seq data, the correlation of stromal cell clusters with survival was explored. The GSVA scores of the cell-specific signature genes of the prognosis-related stromal cell subtypes were calculated and used to stratify eCCA patients. RESULTS: The results revealed that tumor stroma in eCCA were composed of hematopoietic progenitor-like cells (HPLCs), fibroblasts (Fb), Schwann cells (Sch), endothelial cells and immune cells. Prognosis-associated stromal cell subpopulations included MKI67 + HPLC, TMEM158 + C3-Fb, FOXP3 + regulatory T cells (Treg), SLIT2 + Sch, TPSD1 + C2-mast cells (MC) and CTSG + C3-MC. Based on these stromal signatures, the eCCA tumors were categorized into three classes: proliferative Group 1 with enrichment of MKI67 + HPLC, inflammatory and fibrotic Group 2 with enrichment of TPSD1 + C2- MC, FOXP3 + Treg and TMEM158 + C3-Fb, and neuronal Group 3 with enrichment of SLIT2 + Sch and CTSG + C3-MC. ECCA patients in Group 3 had a better prognosis when compared to Group 1 and 2, reflecting different impact of stromal subtypes on tumor progression. CONCLUSION: Single-cell transcriptomic analysis reveals prognosis-related stromal signatures that potentiate the stratification of eCCA into proliferative, inflammatory and fibrotic, and neuronal phenotypes, which has important implications on molecular classification and exploring therapeutic targets in eCCA.