The modern immunotherapy era began with high-dose interleukin-2, which demonstrated that immune activation could produce long-lasting tumor regression in a small proportion of patients with metastatic melanoma and renal cell carcinoma. The arrival of antibodies against CTLA-4, followed by inhibitors of the PD-1 and PD-L1 pathways, transformed that early proof of concept into a central pillar of cancer treatment. These drugs work by interrupting inhibitory signals that restrain T cells. CTLA-4 blockade mainly enhances T-cell priming in lymphoid tissues, while PD-1 or PD-L1 inhibition can restore the function of exhausted T cells within the tumor microenvironment. The results have included unprecedented survival improvements and long-term remission for some people with melanoma, non-small cell lung cancer, kidney cancer, and other malignancies. Yet the benefits remain uneven, and many tumors either never respond or eventually evolve around immune attack.

One of the most important newer targets is LAG-3, an inhibitory receptor found on activated T cells, regulatory T cells, B cells, and natural killer cells. LAG-3 can bind major histocompatibility complex class II molecules and suppress T-cell receptor signaling, proliferation, and production of immune-stimulating cytokines such as interleukin-2 and interferon-gamma. Its expression is particularly prominent in exhausted T cells, suggesting that it may help maintain a dysfunctional immune state inside tumors. The first approved LAG-3-directed therapy, relatlimab, is used with the PD-1 inhibitor nivolumab in advanced or metastatic melanoma. In the RELATIVITY-047 trial, the combination extended median progression-free survival to 10.1 months, compared with 4.6 months for nivolumab alone, and increased the objective response rate from 32.6 percent to 43.1 percent. Severe treatment-related adverse events occurred in 18.9 percent of patients receiving the combination, versus 9.7 percent with nivolumab alone—higher, but generally less frequent than with CTLA-4 and PD-1 combinations.

The LAG-3 story also illustrates why the next generation of immunotherapy will not be a simple succession of universal replacements for older drugs. Relatlimab has shown limited activity in patients whose disease has already progressed on checkpoint inhibitors, with an objective response rate of about 12 percent in one reported setting. Established PD-1 resistance often reflects multiple biological failures, including defective antigen presentation, exclusion of T cells from tumors, altered interferon signaling, and the emergence of immune-suppressive cell populations. Blocking one additional checkpoint may therefore be insufficient once resistance is entrenched. Still, the nivolumab-relatlimab combination has generated interest in earlier disease. Studies in melanoma have reported encouraging pathological responses before surgery, including a 57 percent pathological complete response rate in one neoadjuvant cohort and an 80 percent four-year event-free rate. Other LAG-3 strategies include fianlimab, the immune-activating fusion protein eftilagimod alpha, and bispecific antibodies designed to target both PD-1 and LAG-3 in a single molecule.

Perhaps the most powerful shift is the expansion of immunotherapy beyond the organ where a cancer began. Tissue-agnostic treatment relies on biological features shared across different tumor types, particularly defective DNA mismatch repair and high microsatellite instability. Mismatch repair proteins normally correct small copying errors made during DNA replication. When this system fails, tumors accumulate insertions, deletions, and other mutations, producing abnormal proteins known as neoantigens. These neoantigens can make cancer cells more visible to T cells, increasing the likelihood that PD-1 blockade will work. Deficient mismatch repair can result from inherited mutations associated with Lynch syndrome or from acquired epigenetic silencing, such as methylation of the MLH1 promoter. Clinicians can identify the phenotype using immunohistochemistry, polymerase chain reaction, or next-generation sequencing, allowing treatment decisions to be based on tumor biology rather than anatomical origin.

Tumor mutational burden, which measures the number of somatic mutations per megabase of tumor DNA, offers a related but less reliable signal. The underlying theory is straightforward: more mutations should create more potential neoantigens and therefore more targets for immune recognition. Clinical studies have indeed associated higher mutational burden with improved responses in diseases such as lung cancer and melanoma. However, not every mutation produces an antigen, and not every antigen is displayed effectively by a tumor cell. Measurements also vary between sequencing platforms, differ between tissue and blood samples, and can be distorted by tumor heterogeneity. As a result, mutational burden has not proved consistently dependable as a standalone predictor. A particularly striking subgroup is formed by tumors carrying pathogenic POLE proofreading mutations. These cancers can be ultramutated, densely infiltrated by lymphocytes, and exceptionally responsive to immunotherapy, even when their microscopic appearance suggests aggressive disease.

The clinical consequences of these biomarkers are becoming visible in major trials. In the KEYNOTE-158 study, pembrolizumab produced a response rate of approximately 29 percent in tumors classified as having high mutational burden, compared with 6 percent in tumors without that designation. Responses in mismatch repair-deficient or microsatellite-instability-high cancers were often remarkably durable. In advanced colorectal cancer, the phase 3 KEYNOTE-177 trial showed that first-line pembrolizumab produced a median overall survival of 77.5 months, compared with 36.7 months for chemotherapy, with five-year survival rates of 54.8 percent and 44.2 percent, respectively. The CheckMate-8HW trial further indicated that combining nivolumab with ipilimumab could outperform chemotherapy and nivolumab alone in selected patients, producing a two-year progression-free survival of 72 percent versus 14 percent with chemotherapy. In locally advanced mismatch repair-deficient rectal cancer, neoadjuvant dostarlimab has produced an especially dramatic signal: all 41 patients reported in one study achieved a clinical complete response and entered a watch-and-wait program without immediate surgery or chemoradiotherapy.

That result points toward one of the most provocative possibilities in oncology: replacing automatically scheduled surgery with response-adapted care. The concept is not yet established broadly, and longer follow-up plus prospective randomized evidence remain essential. Nevertheless, highly immunogenic tumors may eventually be managed by treating first, measuring the depth of response, and reserving surgery for residual or recurrent disease. Similar discussions are emerging in melanoma, head and neck cancer, and lung cancer. The approach would represent a profound change in the traditional sequence of cancer care, potentially preserving organs and reducing the complications of major operations. It also raises demanding technical questions. A clinical complete response does not always mean every malignant cell has disappeared, and microscopic residual disease may be difficult to detect with imaging or endoscopy. Future trials will need sensitive molecular monitoring, carefully defined retreatment strategies, and long-term surveillance to determine which patients can safely avoid surgery.

Checkpoint inhibitors are also being combined with established treatments to reshape the tumor environment before immune cells arrive. Chemotherapy can kill cancer cells and release tumor antigens, effectively providing raw material for immune priming. Antiangiogenic drugs can alter abnormal tumor blood vessels, reduce immune suppression, and improve T-cell access. In unresectable liver cancer, atezolizumab plus bevacizumab and the durvalumab-tremelimumab regimen have improved outcomes compared with the former standard, sorafenib. Median overall survival has reached roughly 16.4 to 19.2 months with atezolizumab and bevacizumab, compared with 13.4 to 13.8 months with sorafenib. The choice between regimens can depend on bleeding risk and the safety of vascular endothelial growth factor inhibition. In extensive-stage small-cell lung cancer, adding atezolizumab or durvalumab to platinum-etoposide chemotherapy has delivered the first major advance in decades, extending survival beyond the short-lived responses traditionally produced by chemotherapy alone.

The next wave reaches beyond soluble antibodies and conventional drug combinations. Bispecific antibodies and T-cell engagers can bind a tumor-associated molecule with one arm and a T-cell receptor component with the other, physically bringing immune cells into contact with malignant cells. Antibody-drug conjugates attach potent cytotoxic payloads to tumor-targeting antibodies, concentrating chemotherapy-like activity near cancer cells while potentially limiting exposure elsewhere. Adoptive cell therapies are being adapted for solid tumors through tumor-infiltrating lymphocytes, chimeric antigen receptors, and engineered T-cell receptors. TIL therapy uses a polyclonal population of tumor-reactive lymphocytes expanded from a patient’s own tumor, while CAR and TCR technologies genetically reprogram T cells to recognize selected targets. Engineered cytokines seek to preserve the immune-stimulating effects of interleukin therapies without reproducing their severe systemic toxicity. Personalized vaccines, particularly those directed against patient-specific neoantigens, aim to initiate or strengthen an immune response tailored to the mutations carried by an individual tumor.

Together, these advances reveal an emerging strategy rather than a single miracle treatment. The future of solid-tumor immunotherapy will depend on matching the right immune mechanism to the right biological context, deciding when combinations are more valuable than sequential treatment, and identifying resistance before tumors become clinically obvious. Immune-related toxicities—including pneumonitis, myocarditis, neurological complications, and permanent endocrine damage—remain a major concern as treatment moves into earlier-stage disease, where many patients may already be cured by surgery or other therapies. People with active brain metastases, poor performance status, or a need for corticosteroids have also been underrepresented in pivotal trials. The field is therefore converging on precision immuno-oncology: biomarker testing, response-adapted treatment, engineered molecules, cellular products, and increasingly individualized vaccines. If researchers can make immune attacks more selective and resistance more predictable, therapies once effective only for a minority could become durable, organ-preserving treatments across a much broader range of solid cancers.

One of the most significant strides in biomarker-driven therapy for aUC has been the identification of activating mutations in fibroblast growth factor receptor 3 (FGFR3). These mutations serve as actionable targets for FGFR inhibitors, providing a tailored treatment avenue for a subset of patients whose tumors harbor these specific genetic alterations. This paradigm exemplifies the potential of precision oncology in urothelial carcinoma, where understanding and exploiting tumor genomics can guide therapeutic decisions and potentially enhance clinical outcomes.

On the other hand, the utility of programmed death-ligand 1 (PD-L1) expression as a predictive biomarker for response to ICIs remains unsettled. While PD-L1 tested positive tumors intuitively might be more amenable to immune checkpoint blockade, clinical correlation studies have produced inconsistent and at times conflicting results. These inconsistencies reflect the inherent heterogeneity of PD-L1 expression within tumors, spatial and temporal variability, and technical challenges related to assay standardization and cutoff thresholds, complicating its integration into routine clinical practice.

Beyond FGFR3 mutations and PD-L1 expression, the biomarker landscape in aUC is evolving with several promising candidates emerging. Tumor mutational burden (TMB), a genomic metric quantifying the total number of somatic mutations per coding area of a tumor genome, has garnered considerable interest. A higher TMB is speculated to increase neoantigen generation, potentially enhancing tumor immunogenicity and responsiveness to ICIs. Ongoing investigations are delineating the precise role of TMB in predicting ICI efficacy, although its clinical adoption awaits further validation and consensus on methodological approaches.

Similarly, human epidermal growth factor receptor 2 (HER2) overexpression, well-established in breast and gastric cancers as a therapeutic target, is now being explored in aUC. Amplification or overexpression of HER2 could define an actionable subset amenable to HER2-targeted therapies, including antibody–drug conjugates (ADCs). Preclinical and early clinical data suggest a compelling rationale for this approach, although larger studies are needed to confirm the clinical benefit and define patient selection criteria.

The emergence of circulating tumor DNA (ctDNA) as a minimally invasive biomarker is another transformative development in aUC management. By analyzing tumor-derived genetic material shed into the bloodstream, ctDNA offers a real-time snapshot of tumor genomics and dynamics without the need for invasive biopsies. Increasing evidence supports the prognostic significance of ctDNA levels and its potential to monitor treatment response, detect minimal residual disease, and identify mechanisms of resistance, positioning it as a powerful tool in personalized oncology.

The current review by Coca Membribes, Szabados, and Powles encapsulates these advances, providing a comprehensive synthesis of biomarker-driven strategies in aUC. Their analysis emphasizes the imperative of integrating biomarker assessments into clinical trials and routine care to realize the full potential of targeted and immunotherapeutic agents. Furthermore, they highlight the nuanced biological underpinnings that drive treatment response and resistance, advocating for multidimensional biomarker approaches combining genomic, proteomic, and immunologic parameters.

One challenging aspect in biomarker development lies in the tumor heterogeneity inherent to urothelial carcinoma. This heterogeneity manifests at genetic, epigenetic, and microenvironmental levels, influencing the tumor’s vulnerability to specific therapies. Efforts to characterize inter- and intra-tumoral diversity using cutting-edge single-cell sequencing and spatial transcriptomics are underway, promising to refine biomarker precision and foster novel therapeutic avenues.

Another critical dimension is the dynamic interplay between urothelial tumors and the immune system. The immunosuppressive tumor microenvironment can modulate the efficacy of ICIs, necessitating biomarkers that capture immune contexture beyond mere PD-L1 expression. Functional assays evaluating T-cell infiltration, activation status, and cytokine milieu, alongside novel immune signatures, are under evaluation to better predict and monitor immunotherapeutic responses.

The integration of antibody–drug conjugates into the treatment armamentarium further accentuates the need for biomarkers predictive of efficacy and toxicity. ADCs linked to cytotoxic payloads target specific tumor antigens, warranting accurate assessment of antigen expression and downstream signaling pathways. Identifying biomarkers that stratify patients likely to benefit while minimizing off-target effects remains a subject of intense research.

Emerging data also point towards epigenetic modifications and non-coding RNAs as potential biomarkers and therapeutic targets in aUC. Aberrant DNA methylation patterns, histone modifications, and microRNA expression profiles could offer additional layers of biological insight and may synergize with existing biomarker platforms to drive therapeutic stratification.

The advent of liquid biopsy technologies including, but not limited to, ctDNA, circulating tumor cells (CTCs), and extracellular vesicles expands the biomarker toolkit available for real-time disease monitoring. These minimally invasive modalities can capture tumor evolution and heterogeneity longitudinally, enabling adaptive treatment strategies responsive to tumor dynamics and emerging resistance mechanisms.

Despite these advancements, significant barriers remain before biomarker-driven therapies can achieve widespread clinical impact in aUC. Standardization of biomarker assays, validation across diverse patient cohorts, and integration into clinical workflows present practical challenges. Furthermore, the complex biology of aUC demands combinatorial biomarker approaches that can effectively guide multimodal therapeutic strategies tailored to individual tumor profiles.

In conclusion, the quest for robust biomarkers to guide precision therapies in advanced urothelial carcinoma is gaining momentum, fueled by technological progress and a deeper understanding of tumor biology. Targeted agents against FGFR3 mutations have set a precedent, while biomarker refinement for ICIs, ADCs, and emerging therapies are actively reshaping the treatment paradigm. Circulating tumor DNA and comprehensive molecular profiling hold particular promise in enabling personalized oncology, ultimately improving outcomes for patients afflicted with this aggressive malignancy.

Ongoing collaborative efforts among researchers, clinicians, and industry stakeholders are vital to expedite biomarker discovery, validation, and clinical implementation. As these strategies mature, they will not only optimize therapeutic efficacy but also minimize unnecessary toxicity, heralding a new era of precision medicine in urothelial carcinoma. The clinical community eagerly anticipates forthcoming data to substantiate these promising avenues and translate biomarker-driven treatments into tangible patient benefit.

Subject of Research: Biomarker-driven therapeutic strategies in advanced urothelial carcinoma

Article Title: Towards biomarker-driven therapies for urothelial carcinoma

Article References:
Coca Membribes, S., Szabados, B. & Powles, T. Towards biomarker-driven therapies for urothelial carcinoma.
Nat Rev Clin Oncol (2025). https://doi.org/10.1038/s41571-025-01095-x

Image Credits: AI Generated