HER2 and urothelial carcinoma: current understanding and future directions

Human epidermal growth factor receptor 2 (HER2) has emerged as a crucial biomarker across various cancers, shaping therapeutic strategies and prognostic evaluations. In urothelial carcinoma, HER2 positivity rates can reach up to 68% when HER2-low tumours (immunohistochemistry 1+) are included in the analysis. HER2 overexpression and ERBB2 genomic alterations have been linked to advanced disease stages and poor outcomes in urothelial carcinoma. Emerging evidence suggests that HER2-low tumours might be a distinct and actionable subgroup. Accurate and consistent assessment of HER2 status is increasingly vital to identify patients likely to benefit from HER2-targeted therapies, raising interest in refining thresholds for HER2 expression, aiming to predict treatment response. HER2 heterogeneity across stages and histological subtypes complicates its evaluation, with definitions of HER2 positivity differing between clinical trials and treatments. In urothelial carcinoma, HER2-targeted therapies, such as tyrosine kinase inhibitors, monoclonal antibodies and antibody-drug conjugate (ADCs) have been explored. Unlike tyrosine kinase inhibitors and monoclonal antibodies, which act through HER2-related pathways, ADCs use HER2 as a target but achieve efficacy through additional mechanisms, enabling their activity even at low HER2 expression levels. Trastuzumab deruxtecan, a novel anti-HER2 ADC, has received FDA tumour-agnostic approval for unresectable or metastatic HER2+ solid tumours, including urothelial carcinoma, after prior therapies. Interactions between HER2 protein and putative biomarkers such as EGFR, NECTIN4, PDL1 and FGFR3 genomic alterations might influence therapeutic outcomes, offering opportunities for improved patient selection and innovative combination strategies.