Despite its potential, N4 expression across non-urothelial genitourinary (GU) malignancies remains poorly characterized. Our study aimed to clarify the variability in N4-positivity rates among GU tumors, revealing its heterogeneous expression and dynamic nature.
We analyzed 25 studies evaluating N4 immunohistochemistry (IHC) positivity across different GU malignancies. N4-positivity was highest in urothelial bladder cancer (UBC) with a weighted mean (WM) of 87.1%. A stage-related trend was noted, with metastatic cases exhibiting the highest positivity rates.
Upper tract urothelial carcinoma (UTUC) exhibits lower N4-positivity than UBC with a WM of 62.9%, potentially reflecting differences in tumor biology. Notable variability was observed among histologic subtypes and divergent histologies; for instance, tumors with neuroendocrine or sarcomatoid differentiation almost completely lacked N4 expression.
In non-UC GU malignancies, N4 expression was considerably lower, with WMs of 44.1% in papillary renal cell carcinoma and 18.5% in chromophobe renal cell carcinoma. Interestingly, penile cancer exhibited a relatively high WM of 86.5%, although this finding requires further validation due to the retrospective nature and limited sample size of the studies (Figure 2).

Figure 2: Forrest plot of weighted mean Overall N4 IHC positivity among different subgroups and GU malignancies.
Different studies demonstrated the N4-positivity dynamic nature. Perioperative chemotherapy may downregulate N4 expression, potentially impacting its role as a biomarker. Furthermore, downregulation of N4 has been implicated in resistance to N4-targeting therapies. Tumor site and clinical stage also influence N4 expression, with notable differences between primary tumors and metastases. These findings highlight the importance of longitudinal studies to track N4 expression changes over the disease course and treatment and a standardized assessment methodology to ensure reliable study comparisons.
Understanding the heterogeneity of N4 expression could shape patient selection and optimize therapeutic outcomes. Notably, 20–30% of UC cases are N4-negative, challenging prior assumptions and suggesting its role as a biomarker may be more nuanced than previously thought.

Written by:
- Emanuele Crupi, MD, Department of Medical Oncology, IRCCS University Hospital “Vita Salute” San Raffaele, Milan, Italy
- Daniele Raggi, MD, Department of Genitourinary Medical Oncology, The Royal Marsden Hospital, London, UK