While modern systemic therapies—including immune checkpoint inhibitors such as pembrolizumab and avelumab, as well as the antibody–drug conjugate enfortumab vedotin—have significantly improved outcomes in metastatic urothelial carcinoma (mUC), the evidence supporting their efficacy has largely been derived from populations with pure urothelial histology (pUC). In this context, the present study addresses a relevant clinical gap by evaluating real-world outcomes specifically in patients with UCSD.
Drawing from a large international retrospective dataset including nearly 2000 patients treated across 79 centers, the authors identified 222 cases of metastatic UCSD, representing one of the largest cohorts analyzed to date in this setting. Patients were stratified according to treatment exposure into three clinically meaningful groups reflecting current therapeutic sequencing: avelumab maintenance after platinum-based chemotherapy, pembrolizumab in the post-platinum setting, and enfortumab vedotin following both chemotherapy and immunotherapy. This design allows for a comprehensive overview of treatment effectiveness across the continuum of care in advanced disease.
The most striking and consistent finding of the study is that UCSD is associated with significantly worse outcomes compared to pUC across all treatment modalities. Median overall survival was approximately halved in the UCSD population in each cohort, with particularly pronounced differences observed in the avelumab maintenance setting (13.0 vs 26.8 months) and similarly relevant gaps in the pembrolizumab and enfortumab vedotin cohorts. These differences were not only statistically significant but also clinically meaningful, and were confirmed in multivariable analyses, where UCSD emerged as an independent adverse prognostic factor.
Importantly, the survival disadvantage of UCSD was paralleled by reduced treatment activity. Response rates were consistently lower in patients with squamous differentiation, reaching statistical significance in the pembrolizumab cohort (15% vs 31%), and showing a clear trend in the enfortumab vedotin group as well. Moreover, UCSD was associated with a higher likelihood of primary resistance, particularly to pembrolizumab and enfortumab vedotin, suggesting that these tumors may be intrinsically less sensitive to both immune-mediated and cytotoxic targeted mechanisms.
Another relevant observation is the shorter duration of treatment in UCSD patients, especially in the avelumab and enfortumab vedotin cohorts. Although time on treatment is not a perfect surrogate for progression-free survival, it nonetheless reflects earlier treatment discontinuation, which in this context likely mirrors faster disease progression. Taken together, these findings strongly support the notion that UCSD represents a biologically more aggressive phenotype, characterized by both poorer prognosis and reduced responsiveness to currently available systemic therapies.
Beyond the main results, the study also provides interesting insights into specific subgroups. Notably, female patients with UCSD appeared to derive even less benefit from treatment, with markedly worse survival outcomes compared to their pUC counterparts. While the reasons for this observation remain speculative, the authors appropriately discuss potential biological explanations, including sex-related differences in immune response and the possible influence of hormonal factors. Similarly, patients with tumors originating in the lower urinary tract showed a more pronounced negative impact of squamous differentiation, whereas this effect was less evident in upper tract tumors, which may have distinct molecular features such as higher tumor mutational burden or MSI enrichment.
From a biological perspective, the findings raise important questions regarding the mechanisms underlying treatment resistance in UCSD. Interestingly, prior studies have suggested that tumors with squamous differentiation may exhibit increased infiltration by CD8-positive T lymphocytes, a feature that would theoretically predict enhanced sensitivity to immunotherapy. However, the lack of clinical benefit observed in this and other studies suggests that the immune microenvironment in UCSD may be functionally impaired, possibly due to T-cell exhaustion, immune exclusion, or defective antigen presentation. In parallel, genomic differences—such as higher prevalence of CDKN2A/B alterations—may contribute to both aggressive behavior and resistance to immune checkpoint blockade.
In the context of enfortumab vedotin, reduced expression of Nectin-4 in variant histologies could represent an additional mechanism of resistance, potentially limiting the efficacy of this antibody–drug conjugate in UCSD. Although molecular data were not available in this analysis, these hypotheses are consistent with emerging evidence and highlight the need for integrated translational research.
The strengths of this study lie primarily in its large sample size, international scope, and real-world nature, which enhance the generalizability of the findings. The consistency of the results across different therapeutic settings further reinforces their robustness and clinical relevance. However, several limitations must be acknowledged. The retrospective design inherently introduces the possibility of selection bias, and the absence of centralized pathology review raises concerns regarding the accurate classification and quantification of squamous differentiation. Additionally, the lack of molecular characterization limits the ability to correlate clinical outcomes with underlying biological features. The use of time on treatment instead of progression-free survival is another potential limitation, as it may be influenced by factors unrelated to disease progression, such as toxicity or physician decision-making.
Despite these caveats, the study delivers a clear and clinically meaningful message: squamous differentiation should not be considered a mere histological detail, but rather a key prognostic and potentially predictive factor in metastatic urothelial carcinoma. In daily practice, these findings suggest that patients with UCSD should be recognized as a high-risk population, for whom standard treatment approaches may be less effective. This has important implications not only for patient counseling and clinical decision-making, but also for the design of future clinical trials.
In conclusion, the ARON-2EV analysis convincingly demonstrates that UCSD is associated with inferior outcomes across all major therapeutic classes currently used in advanced urothelial carcinoma. This consistent pattern of reduced survival, lower response rates, and increased primary resistance points toward a distinct and more aggressive disease biology. Moving forward, there is a clear need for prospective studies specifically addressing variant histologies, as well as for the integration of molecular profiling to identify novel therapeutic targets and optimize treatment strategies. Ultimately, a more personalized, histology-driven approach may be required to improve outcomes for this challenging subgroup of patients.
Written by: Veronica Mollica,1 Francesco Massari,1,2 Kazutoshi Fujita,3 Patrizia Giannatempo,4 Enrique Grande,5 Thomas Büttner,6 Maria T Bourlon,7 Tarek Taha,8 Wataru Fukuokaya,9 Zin W Myint,10 Renate Pichler,11 Kirstin Binz,12 Javier Molina-Cerrillo,13 Jindrich Kopecky,14 Alfonso Gómez de Liaño,15 Jakub Kucharz,16 Ondřej Fiala,17,18 Marc R Matrana,19 Ray Manneh Kopp,20 Mattia Alberto Di Civita,21 Anca Zgura,22 Jawaher Ansari,23 Randi Kihnel,19 Francesca De Felice,24 Martín Angel,25 Fernando Sabino M Monteiro,26,27 Andrey Soares,26,28 Yuksel Urun,29 Sebastiano Buti,30,31 Daniele Santini,21 Matteo Santoni,32
- Medical Oncology, IRCCS Azienda Ospedaliero-Universitaria Di Bologna, Bologna, Italy.
- Department of Medical and Surgical Sciences (DIMEC), University of Bologna, Bologna, Italy.
- Department of Urology, Faculty of Medicine, Kindai University, Osaka, Japan.
- Dipartimento Di Oncologia Medica, Fondazione IRCCS Istituto Nazionale Dei Tumori, Milan, Italy.
- Department of Medical Oncology, MD Anderson Cancer Center Madrid, Madrid, Spain.
- Department of Urology, University Hospital Bonn, Bonn, Germany.
- Department of Hemato-Oncology, Escuela de Medicina, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Mexico City, Mexico-Universidad Panamericana, Mexico City, Mexico.
- Royal Marsden NHS Foundation Trust, London, UK.
- Department of Urology, Jikei University School of Medicine, Tokyo, Japan.
- Division of Medical Oncology, Department of Internal Medicine, Markey Cancer Center, University of Kentucky, Lexington, KY, USA.
- Department of Urology, Comprehensive Cancer Center Innsbruck, Medical University of Innsbruck, Innsbruck, Austria.
- Division of Medical Oncology, Department of Internal Medicine, University of Kansas Cancer Center, Kansas, USA.
- Department of Medical Oncology, Hospital Ramón y Cajal, Madrid, Spain.
- Department of Clinical Oncology and Radiotherapy, University Hospital Hradec Kralove, Hradec Kralove, Czechia.
- Medical Oncology Department, CHU Insular-Materno Infantil, Las Palmas, Spain.
- Department of Uro-Oncology, Maria Sklodowska-Curie National Research Institute of Oncology Warsaw, Warsaw, Poland.
- Department of Oncology and Radiotherapeutics, Faculty of Medicine and University Hospital in Pilsen, Charles University, Pilsen, Czech Republic.
- Biomedical Center, Faculty of Medicine in Pilsen, Charles University, Pilsen, Czech Republic.
- Department of Internal Medicine, Hematology/Oncology, Ochsner Medical Center, New Orleans, LA, USA.
- Clinical Oncology, Sociedad de Oncología y Hematología del Cesar, Valledupar, Colombia.
- Department of Radiological, Oncological and Pathological Sciences, Policlinico Umberto I, University of Rome, Rome, Italy.
- Department of Obstetrics-Radiotherapy, Alexandru Trestioreanu Institute of Oncology, "Carol Davila" University of Medicine and Pharmacy, Prof. Dr, Bucharest, Romania.
- Medical Oncology, Tawam Hospital, Al Ain, UAE.
- Radiation Oncology, Department of Radiological, AOU Policlinico Umberto I, Oncological and Pathological Sciences, "Sapienza" University of Rome, Rome, Italy.
- Instituto Alexander Fleming, Ciudad De Buenos Aires, Argentina.
- Latin American Cooperative Oncology Group-LACOG, Porto Alegre, Brazil.
- Oncology and Hematology Department, Hospital Sírio Libanês, Brasília, Brazil.
- Oncology Unit, Hospital Israelita Albert Einstein, São Paulo, SP, Brazil.
- Department of Medical Oncology, Faculty of Medicine, Ankara University, 06620, Ankara, Turkey.
- Medical Oncology Unit, University Hospital of Parma, Parma, Italy.
- Department of Medicine and Surgery, University of Parma, Parma, Italy.
- Medical Oncology Unit, Macerata Hospital, Macerata, Italy.