Abstract: Objective To investigate the molecular subtype specificity of muscle⁃invasive bladder cancer (MIBC) and provide therapeutic guidance for patients with different MIBC molecular subtypes. Methods Based on the UNC molecular typing method for MIBC, transcriptome sequencing data from 48 MIBC patients were used to classify them into two molecular subtypes: Basal and Luminal. Differential expression analysis was performed to explore MIBC⁃specific lncRNAs, followed by further investigation of their molecular characteristics and clinical significance. Combining single⁃cell mass cytometry (CyTOF) and imaging mass cytometry (IMC), the immune microenvironment heterogeneity of Basal subtype MIBC patients with high and low MBNL1⁃AS1 expression was analyzed. Results Molecular subtyping analysis revealed that lncRNA MBNL1⁃AS1 is specifically expressed in MIBC, and its low expression was significantly associated with poor prognosis in the Basal subtype MIBC patients (P=0.022). Further analysis of transcriptome sequencing data revealed that the MBNL1⁃AS1 low expression group in Basal subtype MIBC exhibited characteristics of dedifferentiation (P=0.008), elevated stemness (P=0.020), and high proliferation (P=0.010). The immune score of Basal MIBC patients with low MBNL1⁃AS1 expression showed a significant negative correlation with NK CD56bright cells and Treg cells (P<0.05), while the expression levels of B cell⁃ and CD8+ T cell⁃related genes were elevated in the high MBNL1⁃AS1 expression group. High⁃dimensional single⁃cell proteomics analysis revealed that Basal MIBC patients with low MBNL1⁃AS1 expression exhibited a higher abundance of Treg cells (P=0.016).  Conclusions Basal MIBC patients in the low MBNL1⁃AS1 expression group demonstrated the characteristics of dedifferentiation, elevated stemness, high proliferation, and immune suppression. MBNL1⁃AS1 has the potential to serve as a biomarker for predicting immune response in Basal MIBC. 

Key words: Basal muscle?invasive bladder cancer, MBNL1?AS1, Tumor immune microenvironment