Effect of HER2 and Fascin expression on muscle-invasive bladder cancers: Classification by basaloid and luminal phenotypes

Purpose: The present study aims to identify basaloid and luminal molecular groups and the p53-like sub-group, which is a sub-group of the luminal group, using a specific immunohistochemical panel and investigate human epithelial growth factor receptor 2 (HER2)/Neu and Fascin expression in these groups to analyze their relationship with clinicopathological features and prognosis in a cohort of cases with muscle-invasive urothelial bladder carcinoma (MIBC). Material and Methods: An immunohistochemical panel that included GATA-3, CK20, CD44, and CK5/6 was used to identify molecular sub-groups based on expression in 44 cases of MIBC. HER2/Neu and Fascin expression in basal, luminal, and p53-like groups and the relationship with clinicopathological features and prognosis were investigated. Results: The distribution of the molecular sub-groups determined by immunohistochemistry was as follows: 23 luminal cases (52.3%), 16 basal cases (36.4%), and 5 (11.4%) p53-like cases. There was a statistically significant difference in tumor size across the groups, with the greatest size in the p53-like group (p = 0.001). A statistically significant difference was observed in HER2/Neu expression between the molecular sub-groups (p = 0.017). Comparison of survival and HER2/Neu scores revealed shorter survival in patients with an HER2/Neu score of 3 + compared to those with scores of 0, 1+, and 2+ (p = 0.109). Fascin immunoreactivity was more common in the p53-like and basal groups compared to the luminal group (p = 0.036). Conclusion: Despite the limited number of cases in the MIBC group, our results support that HER2/Neu expression in the luminal sub-group and Fascin expression in basal and p53-like groups may be used as a negative prognostic marker. Multi-center studies that include large case series are warranted in this field.