Classification of muscle-invasive bladder cancer based on tumor stromal compartment

Purpose There has been a resurgence of interest in the tumor stroma in recent years. Whether the relative abundance of various stromal cells can be used as a classification system for muscle-invasive bladder cancer (MIBC) remain elusive.Methods We applied single-cell RNA-sequence (scRNA-seq) data from two MIBCs to identify stromal cell (CD45 negative cells) clusters and the marker gene set of each cell cluster. The single sample gene set enrichment analysis method is used to estimate the relative abundance of the cell clusters in each MIBC sample from The Cancer Genome Atlas. Subsequently, k-means clustering was performed to cluster the MIBCs. Prognosis, oncogenic pathway enrichment score, epithelial-mesenchymal transition (EMT) score, gene mutation frequency, and tumor infiltrating lymphocytes (TILs) were compared among the stromal component-based types of MIBC.ResultsIn the scRNA-seq analysis, a total of nine cell clusters mainly composed of four types of cells were identified. Cell clusters 0, 1, 2, 3, 4, and 7 were considered as bladder epithelial cells, the cells in clusters 5 and 8 were mainly recognized as stem cells and fibroblasts, and the cell cluster 6 was recognized were endothelial cells. The 408 MIBC samples were classified into three types. Type 1 and 3, the “stromal-sufficient” type I and II with higher stromal cells, and Type 2, the “stromal-desert” type with lower stromal cells. The stromal-desert type had significantly better overall survival. As the tumor progresses, the stromal component of the stromal-desert type increases and change into the stromal-sufficient type. Increased stromal cells may come from EMT. The enrichment scores of multiple oncogenic pathways in stromal-sufficient types were significantly higher than those in stromal-desert type. More TILs were found in stromal-sufficient type, but their function may be inhibited by stromal cells. In addition, the three stromal types of MIBC may have specific gene mutation characteristics.Conclusions We proposed a novel stromal component-based classification system to divided into MIBC three phenotype. The three types of MIBC differ in various biological characteristics. The progress of MIBC may be summarized as the process of gradually increasing stromal components and constructing a microenvironment suitable for cancer cells.