The study examined adults with either urothelial carcinoma containing squamous divergent differentiation or pure squamous cell carcinoma of the urinary tract. Urothelial carcinoma begins in the cells lining the bladder and urinary system, whereas pure squamous cell carcinoma is composed entirely of squamous cells, which are flatter, scale-like cells that can emerge after chronic irritation or other biological changes. Both forms are uncommon, and their aggressive behavior has historically left clinicians with limited evidence to guide systemic therapy, particularly after the disease has spread beyond the bladder.

The investigators retrospectively reviewed 49 patients treated with enfortumab vedotin plus pembrolizumab across Mayo Clinic sites. Thirty-five patients, or 71.4 percent, received the combination as their first-line treatment for metastatic disease. Unlike a conventional randomized clinical trial, the analysis relied on medical records and imaging performed during routine care. Tumor responses were assessed retrospectively from a mixture of computed tomography, magnetic resonance imaging, and positron emission tomography reports rather than through a uniform, prospective RECIST 1.1 evaluation. This distinction is crucial because real-world imaging schedules and reporting practices can vary considerably.

Even with those limitations, the reported activity was striking. Twenty-nine patients, representing 59.2 percent of the cohort, achieved a complete response, meaning that no detectable disease remained on follow-up imaging. Four additional patients, or 8.2 percent, experienced a partial response, while another four had stable disease. Twelve patients, or 24.5 percent, had progressive disease. Taken together, the retrospectively adjudicated objective response rate was 67.3 percent, although the unusually high proportion of complete responses should be interpreted cautiously because of the study’s small size, retrospective design, and potential differences in how patients were selected and followed.

The treatment combines two distinct biological strategies. Enfortumab vedotin is an antibody–drug conjugate, a targeted therapy designed to carry a potent cell-killing drug directly to tumor cells. Its antibody component recognizes Nectin-4, a protein commonly found on the surface of urothelial cancer cells. After binding, the cancer cell internalizes the drug complex, allowing the attached cytotoxic payload to disrupt cellular structures involved in division and survival. Pembrolizumab works differently: it blocks the PD-1 immune checkpoint, a molecular “brake” that tumors can exploit to suppress T cells. By releasing that brake, the drug may help the immune system identify and attack malignant cells.

The two agents may therefore create a complementary assault. Enfortumab vedotin can directly damage tumor cells, while the resulting tumor-cell death may expose cancer-associated signals to the immune system. Pembrolizumab may then enhance T-cell activity against residual disease. However, the study was not designed to prove how the combination works in squamous tumors, and the biological behavior of these cancers may differ from conventional urothelial carcinoma. Squamous differentiation could influence Nectin-4 expression, immune-cell infiltration, or the tumor’s capacity to evade immune attack, making laboratory and translational research an essential next step.

Patients who responded also appeared to benefit for a meaningful period. The median duration of response was 23.7 months, with a 95 percent confidence interval extending from 16.0 months to a point that had not yet been reached. Median overall survival was 24.5 months, while median progression-free survival was 23.8 months. Overall survival measures the time until death from any cause, whereas progression-free survival measures the time until the cancer worsens or the patient dies. Because confidence intervals for survival estimates extended to “not reached,” some outcomes remained immature at the time of analysis, meaning that longer follow-up could change the precise estimates.

The clearest prognostic factor was the amount of metastatic disease. In multivariable analysis, each additional metastatic site was associated with a higher risk of death, with a hazard ratio of 2.37 and a 95 percent confidence interval of 1.55 to 3.62. A hazard ratio above one indicates greater risk, and the reported association was statistically strong, with a p-value below 0.001. In practical terms, the results suggest that the burden and distribution of metastatic cancer may matter more for survival than the presence or extent of squamous differentiation itself. Still, this interpretation is exploratory and cannot establish that metastatic burden directly causes poorer outcomes.

The researchers found no statistically discernible survival difference based on how extensively the tumor showed squamous divergent differentiation. Yet the comparison was underpowered because the overall cohort contained fewer than 50 patients and the disease subgroups were small. The study also included limited pretreatment testing for Nectin-4: only 12 patients had available analyses. Those results were descriptive rather than definitive, so they cannot determine whether Nectin-4 levels predict response to enfortumab vedotin. This is particularly important because a biomarker that helps select patients could be valuable in a rare cancer where treatment decisions are often made with incomplete evidence.

The findings arrive as enfortumab vedotin plus pembrolizumab becomes an increasingly important treatment strategy for advanced urothelial carcinoma, but they should not be mistaken for proof that every squamous bladder cancer will respond. The investigators emphasize that their data come from a single health-care system, lack a control group, and were generated through retrospective review of heterogeneous clinical records. Selection bias may have favored patients healthy enough to receive combination therapy, while inconsistent imaging could have affected response classification. Nevertheless, the study provides one of the more substantial real-world datasets for this neglected population and suggests that squamous histology alone should not automatically exclude patients from consideration of the regimen. Prospective multicenter research, standardized response assessment, longer follow-up, and integrated Nectin-4 and immune profiling will be needed to determine which patients are most likely to experience durable benefit.

Subject of Research: Enfortumab vedotin plus pembrolizumab in urothelial carcinoma with squamous divergent differentiation and pure squamous cell carcinoma

Article Title: Real-world outcomes and prognostic determinants of enfortumab vedotin plus pembrolizumab in urothelial carcinoma with squamous divergent differentiation and pure squamous cell carcinoma

Article References: Zarka, J., Tabiim, A., Lucien, F. et al. “Real-world outcomes and prognostic determinants of enfortumab vedotin plus pembrolizumab in urothelial carcinoma with squamous divergent differentiation and pure squamous cell carcinoma.” Cancer Immunology, Immunotherapy (2026).

Image Credits: AI Generated

DOI: 10.1007/s00262-026-04535-4

Keywords: Urothelial carcinoma; squamous cell carcinoma; squamous divergent differentiation; enfortumab vedotin; pembrolizumab; antibody–drug conjugates; immunotherapy; Nectin-4; treatment outcome; metastatic cancer

Urothelial carcinoma can arise in the bladder, ureters, renal pelvis, or urethra and is frequently diagnosed when it has already invaded surrounding tissue or spread to distant organs. For many years, platinum-based chemotherapy formed the backbone of treatment for advanced disease, but its effectiveness is limited by resistance, relapse, and the health status of patients who may be older or affected by kidney impairment and other illnesses. The combination examined in GUARDIANS brings together two distinctly engineered medicines. Enfortumab vedotin is an antibody–drug conjugate that recognizes Nectin-4, a protein commonly present at high levels on urothelial cancer cells, while pembrolizumab is an immune checkpoint inhibitor that helps restore the capacity of T cells to attack malignant cells.

Enfortumab vedotin operates as a molecular delivery system. Its antibody component binds to Nectin-4 on the tumor-cell surface and is internalized, carrying with it the cytotoxic payload monomethyl auristatin E, or MMAE. Once released inside the cell, MMAE disrupts microtubules, structures required for cell division, eventually triggering cell death. Pembrolizumab works through a different pathway. Tumors can suppress immune activity by engaging the PD-1 receptor on T cells through its ligands, PD-L1 and PD-L2. By blocking PD-1, pembrolizumab can release this inhibitory signal. The combination therefore pairs direct drug-mediated killing with immune reactivation, a strategy that may produce complementary or synergistic antitumor effects.

The importance of the GUARDIANS analysis lies in its real-world design. Randomized trials are essential for establishing whether a treatment works under standardized conditions, but participants in those studies are often selected according to strict criteria involving organ function, performance status, previous therapies, and the absence of serious coexisting disease. Routine clinical practice is less predictable. Physicians treat patients with varying levels of frailty, diverse patterns of metastasis, different prior treatments, and medical conditions that may influence both benefit and toxicity. By assembling data from multiple institutions, the GUARDIANS investigators sought to determine whether the clinical promise of enfortumab vedotin plus pembrolizumab remained visible when the regimen was used across a wider spectrum of patients.

The study’s central assessment focused on effectiveness and safety, the two measures that ultimately determine whether a cancer therapy can be integrated into routine care. Effectiveness in this setting is generally evaluated through outcomes such as tumor response, disease control, progression-free survival, and overall survival. These measures address different questions: whether tumors shrink, how long the cancer remains stable or controlled, how quickly the disease progresses, and how long patients live after treatment begins. Safety analysis examines treatment-related adverse events, dose interruptions, reductions, and discontinuations. Such details are particularly important for a combination in which adverse effects can arise from either the antibody–drug conjugate, the immune therapy, or the interaction between treatment and a patient’s underlying vulnerabilities.

The findings provide real-world support for the clinical activity of the combination in advanced urothelial carcinoma, while also illustrating the practical toxicities that oncologists must manage. The regimen is not a simple infusion with a uniform risk profile. Enfortumab vedotin can be associated with peripheral neuropathy, skin reactions, fatigue, appetite changes, hyperglycemia, and ocular complications, reflecting the effects of its cytotoxic payload and its distribution through the body. Pembrolizumab can produce immune-related inflammation affecting organs such as the thyroid, lungs, liver, colon, kidneys, or skin. These reactions occur when immune activation extends beyond the tumor and can require corticosteroids, treatment interruption, or permanent discontinuation in serious cases.

The real-world perspective is especially relevant for patients who would not necessarily resemble the participants in the pivotal trials that established the combination. Advanced urothelial carcinoma commonly affects older adults, many of whom have reduced renal function because of age, previous surgery, urinary obstruction, or other chronic disease. Some have received earlier chemotherapy or immunotherapy, while others begin treatment with extensive metastatic disease and limited physical reserve. Observational cohorts cannot replace randomized comparisons because treatment decisions are not assigned by chance and may be influenced by disease severity or physician preference. However, they can reveal how treatment selection, dose management, and adverse-event monitoring function in the environment where most patients actually receive care.

The GUARDIANS results also contribute to a broader shift in the therapeutic logic of urothelial cancer. Instead of relying exclusively on sequential treatment—first chemotherapy, then immunotherapy, followed by a targeted agent—clinicians increasingly use biologically complementary combinations earlier in the disease course. The rationale is to expose cancer cells to multiple pressures before resistant clones become dominant. Yet combination therapy also raises an important clinical question: does improved tumor control come at the cost of tolerability? Real-world evidence can help answer that question by documenting how often patients require modifications, whether toxicity accumulates over time, and which baseline characteristics may identify people more likely to benefit or experience complications.

For patients and physicians, the practical message is not that enfortumab vedotin plus pembrolizumab is universally suitable, but that it has become a significant treatment option whose value depends on careful selection and active monitoring. Before and during therapy, clinicians may need to assess blood glucose, neurologic symptoms, skin changes, vision, liver function, thyroid activity, and signs of immune-mediated inflammation. Early recognition can be decisive: neuropathy may require dose adjustment, severe rash may demand interruption, and immune-related organ injury may need prompt immunosuppression. The regimen’s effectiveness must therefore be considered alongside the patient’s performance status, comorbidities, previous treatment exposure, goals of care, and ability to attend frequent monitoring visits.

As the GUARDIANS cohort adds evidence from routine practice, it strengthens the case for continuing to study how this dual-action treatment performs across different populations and health systems. Future research will need to clarify which molecular features predict response, whether specific metastatic sites behave differently, how long treatment should continue, and how the combination compares with emerging antibody–drug conjugates and other targeted therapies. Long-term follow-up will also be important for understanding delayed immune toxicities, persistent neuropathy, and outcomes after treatment discontinuation. For now, the multi-institutional experience places enfortumab vedotin plus pembrolizumab among the most consequential developments in advanced urothelial carcinoma, while emphasizing that the success of precision oncology depends not only on attacking the cancer, but also on managing the patient.

Subject of Research: Effectiveness and safety of enfortumab vedotin plus pembrolizumab in a real-world population with urothelial carcinoma.

Article Title: Effectiveness and safety of enfortumab vedotin and pembrolizumab in a real-world patient population with urothelial carcinoma: results from a multi-institutional cohort (GUARDIANS)

Article References: Published in Cancer Immunology, Immunotherapy; DOI: 10.1007/s00262-026-04448-2

Image Credits: AI Generated

DOI: 10.1007/s00262-026-04448-2

Keywords: Urothelial carcinoma, bladder cancer, enfortumab vedotin, pembrolizumab, antibody–drug conjugate, immune checkpoint inhibitor, Nectin-4, PD-1, real-world evidence, GUARDIANS cohort, cancer immunotherapy, treatment safety