Keratins and desmosomal proteins: Utility for molecular subtype identification in muscle-invasive bladder cancer

Keratins (CK) and desmosomal proteins are associated with prognosis in many cancers, and CK5, CK14 and CK20 are recognized as surrogate markers for molecular subtyping of muscle-invasive bladder cancer (MIBC). We analyzed the correlation between protein clustering and MIBC subtypes. We retrieved samples of muscle-invasive UC from patients treated with radical cystectomy without prior neoadjuvant therapy at two institutions. Immunohistochemical staining with tissue microarrays was performed for keratins (CK5, CK7, CK8, CK10, CK13, CK14, CK17, CK18, CK19, CK20), desmogleins (DSG2, DSG3) and desmocollin 3 (DSC3), and outcomes were evaluated using the H-Score. Molecular classification subgroups were defined according to CK5 and CK20 expression; for a subset of cases, the MDACC molecular classification was also available. Clinical data were retrieved from medical records. Hierarchical clustering with Euclidean distance, classification trees and principal component analysis was used for data visualization. We identified protein clustering patterns for luminal and basal subtypes in 232 analyzed samples. DSG2 groups were independent from DSC3 and DSG3 clustering in the luminal subtype. The molecular clusters were comparable in matched primary tumour and lymph node metastases (LNM) samples, and the protein expression correlated moderately with each other. CK5 (PT (90 [IQR 8.3-265, LNM (30.8 [IQR 6.7-155]; p = 0.011)), CK17 (PT (145 [IQR 42.5-222.5]),LNM (47.5 [IQR 14.2-110]; p = 0.005), DSG2 ( PT (55 [IQR 15-105]), LNM (32.1 (7.5-75.8)); p = 0.004), and DSC3 (PT (20.8 [IQR 0-71.7]), LNM (3.8 [IQR 0-43.3]; p = 0.013) expression were lower in LNM. Limitations include the absence of patients treated with neoadjuvant therapy and the risk of overfitting. We concluded that distinct keratin and desmosomal protein patterns are linked to cancer subtypes, and remain consistent in LNM. These findings indicate potential for keratins and desmosomal proteins to guide muscle-invasive bladder cancer subtype classification with possible prognostic implications, necessitating further research.