Knowledge mapping of photodynamic therapy in bladder cancer: a bibliometric analysis (2000–2025)

Introduction

Bladder cancer (BC) is a common malignancy worldwide. Its high incidence and recurrence rates pose a serious threat to patients’ health (1,2). BC ranks as the sixth most common cancer in men (3) and among the top ten cancers globally in terms of overall burden (4), with particularly high incidence rates in developed countries such as Germany (5). Traditional treatments such as transurethral resection, intravesical chemotherapy, and immunotherapy are widely used in the treatment of BC; however, many patients face both treatment failure and tumor recurrence. Thus, novel treatment strategies urgently need to be developed (6,7).

In contrast to traditional therapies, photodynamic therapy (PDT), a selective treatment based on the interaction of photosensitizers, light, and oxygen, has shown significant progress in the treatment of BC. PDT induces cell death by the selective retention and activation of photosensitizers in tumor tissues. These photosensitizers are activated by light of specific wavelengths to produce reactive oxygen species (ROS) (6,8,9). Clinical studies have shown the high efficacy of PDT, with overall response rates exceeding 80% for non-muscle-invasive BC, especially in relapsed and refractory cases (10). In addition, the development of novel photosensitizers, such as tetrahydroporphyrin-tetramethylenesulfonate, which uses near-infrared light to achieve deeper tissue penetration, offers new possibilities for the treatment of muscle-invasive BC (5). Despite challenges related to dosage optimization and side-effect management, ongoing clinical research is expanding the potential of PDT as a second-line or adjuvant therapy by improving treatment protocols and outcomes (11).

Bibliometrics is a methodological approach for analyzing literature, enabling both the quantitative and qualitative assessments of publication outputs and trends in a specific research domain (12,13). This analytical process provides comprehensive data on authors, keywords, journals, countries, institutions, and references related to the field of study (14,15). Bibliometric tools such as CiteSpace (16), VOSviewer (17), the R package “bibliometrix” (18), and Python (19) are commonly used to visualize literature analysis outcomes. These tools have gained extensive application across various medical disciplines, including oncology (20,21), orthopedics (22,23), thoracic surgery (24), rheumatology (25), and precision medicine (26). To the best of our knowledge, previous bibliometric investigations have been conducted on PDT in endodontics (27), renal medicine (28), skin cancer (29), eye diseases (30), and oral science (31). A previous bibliometric analysis on the application of PDT in BC indicated that future research should focus on in situ cancer detection, the development of novel photosensitizers, the optimization of drug delivery systems, and long-term follow-up (32). Building on previous studies, this analysis extended the time frame from 2000 to the present, and adopted an updated literature dataset. It also explored under-investigated areas, including nanotechnology, combination therapy strategies involving PDT and other treatments, and approaches integrating diagnosis with treatment. Our findings revealed emerging trends in research on PDT in BC. We present this article in accordance with the BIBLIO reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2026-1-0122/rc).

Methods

Search strategy

On October 31, 2025, a comprehensive literature search was performed of the Web of Science Core Collection (WoSCC) database (accessible at https://www.webofscience.com/wos/woscc/basic-search) using the following search strategy: TS=((“photodynamic therapy” OR PDT OR “photodynamic treatment” OR “photoimmunotherapy” OR “light-activated therapy” OR “photosensitizer*”) AND (“bladder cancer” OR “urinary bladder neoplasm*” OR “bladder tumor*” OR “bladder carcinoma” OR “urothelial carcinoma” OR “transitional cell carcinoma”)) AND LA=(English). The document types were restricted to “articles” and “reviews” (Figure 1).

Figure 1 Flowchart of the publication screening process.

Data analysis

VOSviewer (version 1.6.20) is a bibliometric analysis software program that can extract key information from numerous publications (33). It is often used to build collaboration, co-citation, and co-occurrence networks (34,35). In the present study, the software was used to complete the following analyses: country and institution analysis, journal and co-cited journal analysis, author and co-cited author analysis, and keyword co-occurrence analysis. In the maps produced by VOSviewer, a node represents an item such as the country, institution, journal, and author, while the node size and color indicate the number and classification of these items, respectively, and the line thickness between nodes reflects the degree of collaboration or co-citation of the items (36,37).

CiteSpace (version 6.4.R1) is a software program developed by Professors Chen C for bibliometric analysis and visualization (38-40). In our study, CiteSpace was applied to map the dual-map overlay of journals and to analyze references with citation bursts.

The R package “bibliometrix” (version 4.4.1) (https://www.bibliometrix.org) was used to perform a thematic evolution analysis and to construct a global publication network of PDT in BC. The quartile and impact factor (IF) of each journal were obtained from Journal Citation Reports 2023.

Results

Quantitative analysis of publication

According to our search strategy, a total of 595 studies on PDT in BC had been conducted in the past 26 years, including 443 “articles” and 152 “reviews”. As shown in Figure 2, based on the growth rate of the number of publications each year, the whole period can be divided into three parts: Period I [2000–2015], Period II [2016–2020], and Period III [2021–2025]. In Period I, research on PDT in BC was still in the exploration phase; the level of research activity was greatly affected by individual projects or events, and a stable research scope had not yet been established. During Period II, the volume of publications increased steadily and continuously, signifying the onset of a phase characterized by rapid advancements in the field. This growth garnered sustained interest from an increasing number of researchers. In Period III, the field appears to have reached a relatively mature stage, with mainstream research directions established, and the annual publication volumes stabilizing. Looking ahead, the annual volume of publications in this field is expected to remain high and stable in the next few years, with a relatively low likelihood of explosive growth.

Figure 2 Annual research output on photodynamic therapy in bladder cancer.

Country and institutional analysis

The identified studies originated from 42 countries and 124 institutions. The leading 10 nations were located across Europe, Asia, and North America, with the majority situated in Europe (n=6) and Asia (n=3) (Table 1). China contributed the highest number of publications (n=137, 23.0%), followed by the United States (n=106, 17.8%), Germany (n=55, 9.2%), and Japan (n=43, 7.2%). The combined publications from China, the United States, and Germany accounted for almost half of the total publications (48.0%).

To analyze the collaborations, we filtered and visualized 42 countries with at least two publications and constructed a collaborative network based on the number of publications and co-authorship relationships among these countries (Figure 3). Notably, extensive and active international collaborations were evident among various countries. For example, China maintained close research partnerships with the United States, Germany, Japan, and Canada. Similarly, the United States engaged in active collaborative efforts with China, the United Kingdom, France, and Germany.

Figure 3 Geographical distribution (A) and country/region-level visualization (B) of research on photodynamic therapy in bladder cancer.

The top 10 institutions were distributed across six countries, demonstrating a relatively decentralized geographical pattern. Among these, four institutions contributed the highest number of relevant publications: National University of Singapore (n=28, 4.7%), Katholieke Universiteit Leuven (n=22, 3.7%), German Cancer Research Center (n=21, 3.5%), and Universidade de Coimbra (n=21, 3.5%). Subsequently, 124 institutions with at least three publications were selected for visualization. A collaborative network based on the number of publications and co-authorship ties among these institutions was then constructed (Figure 4). As shown in Figure 4, a strong collaborative network was observed among the National University of Singapore, Singapore General Hospital, and Nanyang Technological University. Similarly, active partnerships were observed between Katholieke Universiteit Leuven, Centre Alexis Vautrin, and Université Catholique de Louvain. Further, close research cooperation was observed between Universidade de Coimbra and the University of Aveiro.

Figure 4 Visualization of institutions conducting research on photodynamic therapy in bladder cancer.

Journals and co-cited journals

Research on PDT in BC has been published across 97 scholarly journals. Photodiagnosis and Photodynamic Therapy published the most articles (n=35, 5.9%), followed by Photochemistry and Photobiology (n=27, 4.5%), the Journal of Urology (n=19, 3.2%), and the Journal of Photochemistry and Photobiology B: Biology (n=18, 3.0%). Among the top 10 journals, the Journal of Urology had the highest IF (IF =7.6), followed by BJU International (IF =5.8). To further analyze the publication landscape, we screened the 97 journals for those with at least two relevant publications and constructed a citation network (Figure 5A). As Figure 5A shows, Photodiagnosis and Photodynamic Therapy had ongoing citation relationships with the Journal of Urology, Photochemistry, and Photobiology, and Biomedicine and Pharmacotherapy.

Figure 5 Visualization of journals (A) and co-cited journals (B) for research on photodynamic therapy in bladder cancer.

As shown in Table 2, of the top 10 co-cited journals, three publications each garnered more than 800 citations. The Journal of Urology (co-citation =1,899) was the most frequently cited, followed by Photochemistry and Photobiology (co-citation =1,293) and the Journal of Photochemistry and Photobiology B: Biology (co-citation =889). In addition, European Urology had the highest IF (IF =23.4), followed by Biomaterials (IF =14.0), and Cancer Research (IF =11.2). Further, to visualize the co-citation patterns, journals with a minimum co-citation threshold of 50 were included in a co-citation network (Figure 5B). As shown in Figure 5B, the Journal of Immunology had robust co-citation connections with European Urology, Urology, BJU International, and several other journals.

The dual-map overlay of journals revealed the citation relationships between journals and co-cited journals, with clusters of citing journals positioned on the left and clusters of cited journals on the right (41,42). As illustrated in Figure 6, a prominent “knowledge triangle” (comprising mathematics/computational science, physics/chemistry/materials science, and life sciences) was observed, highlighting several key interdisciplinary areas in modern scientific research: nanoscience and technology, biophysics and biochemistry, and computational biology and bioinformatics.

Figure 6 Dual-map overlay of journals for research on photodynamic therapy in bladder cancer.

Authors and co-cited authors

A total of 2,907 authors contributed to research on PDT in BC. Among the top 10 authors, two individuals each contributed 18 publications (Table 3). A co-authorship network was constructed, including only those authors with four or more published articles (Figure 7A). Olivo Malini, Fernandes Rosa, De Witte Pam AM, Inoue Keiji, and Gederaas Odrim A had the largest nodes in the network, representing the authors with the highest number of publications on PDT in BC. Moreover, close collaborations among multiple authors were observed. For example, De Witte Pam AM collaborated closely with Roskams T, Olivo Malini, and Bhuvaneswari Ramaswamy, while Fernandes Rosa collaborated closely with Pereira Patricia M R and other researchers.

Figure 7 Visualization of authors (A) and co-cited authors (B) for research on photodynamic therapy in bladder cancer.

Among the 17,090 co-cited authors, nine individuals had over 100 co-citations (Table 3). The most frequently co-cited author was Dougherty, TJ (n=202), followed by Kriegmair, M (n=178) and Nseyo, UO (n=160). Authors with a minimum of 26 co-citations were included in the co-citation network (Figure 7B). As illustrated in Figure 7B, active collaborative relationships were evident among several co-cited authors, including Dougherty TJ, Allison RR, Kriegmair M, and Waidelich R.

Co-cited references

Over the past 26 years, 24,250 co-cited references on research on PDT in BC have been published. Among the top 10 co-cited references (Table 4), each was co-cited a minimum of 47 times, with one reference (34) exceeding 80 co-citations. References with co-citation frequencies of 15 or higher were included in the co-citation network diagram (Figure 8). As illustrated in Figure 8, Dougherty TJ (1998, JNCI: Journal of the National Cancer Institute) exhibited robust co-citation linkages with Dolmans DEJ (2003, Nat Rev Cancer: Nature Reviews Cancer), Kriegmair M (1996, Br J Urol: British Journal of Urology), and Kennedy JC (1990, J Photochem Photobiol B: Journal of Photochemistry and Photobiology B: Biology), among others.

Figure 8 Visualization of co-cited references for research on photodynamic therapy in bladder cancer.

References with citation bursts

Citation bursts of references reflect a surge in citations in a specific research domain over a defined timeframe. In this analysis, CiteSpace was employed to identify 20 such references demonstrating pronounced citation bursts (Figure 9). Each bar in Figure 9 corresponds to a calendar year, with the red bars signifying periods of intense citation activity (53,54). Citation bursts were observed as early as the year 2000 and as recently as 2022. The reference exhibiting the most pronounced citation burst (strength =11.23) was the study titled “Photodynamic therapy of bladder cancer: A phase I study using intravesical administration of 5-aminolaevulinic acid (5-ALA) for the photosensitization of tumor tissue”, published by Lange et al. This work experienced a significant surge in citations from 2000 to 2004. The second most prominent citation burst in the references (strength =10.21) was titled “A novel photosensitizer for photodynamic therapy induces endoplasmic reticulum stress-mediated cell death in lung cancer”, published in Theranostics by Lin et al., with citation bursts from 2019 to 2023. Overall, the burst strengths of these 20 references ranged from 6.67 to 11.23, and the durations of the citation bursts ranged from 2 to 5 years.

Figure 9 Top 20 references with strong citation bursts. A red bar indicates high citations in that year.

Hotspots and frontiers

Keyword co-occurrence analysis enables the rapid identification of research hotspots in a specific field. Table 5 presents the top 20 high-frequency keywords in studies on PDT in BC. Among these, hypericin (HYP) and 5-ALA each appeared approximately 40 times, indicating that they represent the primary research fronts in this area.

We selected keywords that appeared at least four times and conducted the cluster analysis using VOSviewer (Figure 10A). The thickness of the connecting lines between nodes indicates the strength of the associations. As illustrated in Figure 10A, a total of six clusters were identified, corresponding to five distinct research fronts. The purple cluster includes keywords such as PDT, ROS, singlet oxygen, and phthalocyanines. The red cluster includes terms such as BC, immunotherapy, chemotherapy, and intravesical therapy. The green cluster includes keywords such as nanotechnology, nanoparticles, porphyrin, and tumor microenvironment (TME). The blue cluster includes keywords such as photodynamic diagnosis (PDD), protoporphyrin IX (PPIX), photosensitizers, and HYP. The yellow cluster includes keywords such as fluorescence, photodynamic, apoptosis, and autophagy.

Figure 10 Keyword cluster analysis (A) and trend topic analysis (B). PDD, photodynamic diagnosis; PPIX, protoporphyrin IX.

The trend topic analysis of the keywords (Figure 10B) showed that from 2002 to 2010, research mainly focused on the basic mechanisms of disease, fluorescent agents, and photosensitizers. The main keywords during this period were transitional cell carcinoma (TCC), bladder, fluorescence, radiosensitizer, and Photofrin II. From 2010 to 2018, the research focus shifted toward technology convergence and innovation, with the main keywords including photochemotherapy, autophagy, PDT, and phthalocyanines. Additionally, four keywords—immunotherapy, immunogenic cell death (ICD), nanotechnology, and nanoparticles—appeared frequently in the past seven years [2018–2024], indicating current research hotspots for PDT in BC.

Discussion

General information

This bibliometric analysis delineates the evolving landscape and structural dynamics of PDT research in BC over the past quarter-century. The findings reveal not only quantitative growth but also distinct patterns in geographic contribution, institutional collaboration, and knowledge dissemination.

The temporal evolution of publication output signifies a clear maturation of the research field. The initial period of fluctuating productivity [2000–2015] reflected an exploratory phase, heavily dependent on individual projects. This transitioned into a phase of sustained growth [2016–2021], indicating the establishment of PDT as a recognized and actively pursued therapeutic avenue in bladder oncology. The subsequent stabilization at a high publication volume [2022–2025] suggests the field has reached a plateau of maturity, with core research themes now well-defined and attracting consistent scholarly attention.

While China and the United States are the undisputed volume leaders in publication output, their dominance is not reflected at the institutional level, as no single institution from these countries ranks among the top 10 most productive. This points to a highly decentralized research infrastructure within these nations, with efforts distributed across numerous centers. Conversely, countries like Portugal demonstrate a model of concentrated excellence; despite a lower national publication count, multiple Portuguese universities (e.g., University of Coimbra, Aveiro, Lisbon) feature prominently among leading institutions, indicating focused and potent research clusters.

The analysis identifies active collaborative networks, particularly among the United States, China, Canada, and Singapore at the country level, and within specific institutional clusters (e.g., the Singaporean consortium). However, these connections appear selective rather than pervasive. Notably, some highly productive institutions (e.g., Katholieke Universiteit Leuven) show limited external collaboration. Furthermore, inter-institutional links between major contributing countries like the U.S. and China remain relatively underdeveloped. This relative insularity may impede the cross-pollination of ideas and slow the pace of translational innovation, highlighting an area for strategic improvement.

The publication and citation patterns reveal a strategic dichotomy in knowledge dissemination. Photodiagnosis and Photodynamic Therapy, a specialized Q2 journal, serves as the primary outlet for direct research output, underscoring the field’s technical specificity. In contrast, the foundational knowledge base is anchored in high-impact, broad-scope clinical journals such as The Journal of Urology and European Urology (Q1). This indicates that while researchers prioritize venue relevance for disseminating new findings, they rely on established, authoritative clinical literature to ground their work, bridging specialized innovation with mainstream urological oncology.

The identification of leading authors (e.g., Fernandes, Olivo) and foundational, highly co-cited references (e.g., Dougherty et al., 1998) maps the intellectual pillars of the field. These key contributors and seminal papers have established the fundamental paradigms, photosensitizer protocols, and clinical proof-of-concept that continue to guide and catalyze contemporary research.

Knowledge base

A co-cited reference is defined as a publication that is cited simultaneously in multiple other articles, thereby serving as a foundational element in a particular research domain (55). In this bibliometric analysis, we identified the 10 most frequently co-cited references to establish the core research foundation for PDT in the context of BC.

Hotspots and frontiers

Our bibliometric analysis, through keyword co-occurrence, cluster analysis, and detection of references with citation bursts, provides a dynamic map of the intellectual structure and its evolution in PDT research for BC. The findings move beyond listing topics to reveal a clear trajectory: from foundational work on photosensitizer mechanisms to their clinical translation, and more recently, towards innovative combinatorial strategies integrating nanotechnology and immunotherapy.

Evolution of core research themes: from photosensitizer fundamentals to clinical translation

The keyword and reference analyses reveal a non-random evolution of research focus. The initial phase (approximately 2000–2010), as indicated by early citation bursts and predominant keywords like “fluorescence” and “Photofrin” was predominantly dedicated to establishing the basic photobiology and early clinical proof-of-concept. Seminal work, such as that by Benson et al., demonstrated the selective accumulation of hematoporphyrin derivative (HpD) in bladder tumors, laying the critical groundwork for the field (56,57). The high and sustained co-citation of foundational papers [e.g., Dougherty et al., 1998 (43); Kennedy et al., 1990 (49)] further solidifies this period as the knowledge base.

Subsequently, the research front shifted decisively towards optimizing and clinically translating specific, improved agents, as directly evidenced by the emergence and high frequency of keywords: “hypericin”, “5-aminolevulinic acid” and “protoporphyrin IX” (Table 5). Research crystallized around understanding their distinct properties. Comparative studies highlighted hypericin’s strong fluorescence and potent phototoxicity in vitro (58,59), while investigations into 5-ALA focused on its metabolism to PPIX and its application in fluorescence-guided diagnosis, a key reason for its strong keyword association with “photodynamic diagnosis” (60). This phase was characterized by moving from general principles to optimizing specific agents for better selectivity and dual diagnostic-therapeutic applications.

Crucially, this translational focus included robust preclinical validation in BC models. Studies by Larsen et al. and Lucroy et al. in rat and canine models, respectively, were pivotal in demonstrating the dose-dependent induction of PPIX fluorescence and the efficacy and safety of 5-ALA/PPIX-based PDT, establishing vital preclinical platforms (61,62). Further work by Rahman et al. advanced this by successfully combining PPIX-PDT with novel prodrugs in orthotopic models (63). These collective efforts represent the critical bridge from in vitro optimization to in vivo validation, defining a major thematic branch in the field’s evolution.

The rise of convergent frontiers: nanotechnology and immunotherapy

The most striking trend identified is the recent, convergent emergence of nanotechnology and immunotherapy as dominant frontiers. The trend topic analysis (Figure 10B) objectively shows that keywords “nanoparticles”, “nanotechnology”, “immunotherapy” and “immunogenic cell death” have sharply increased in prominence over the past seven years (2018–2025). Their close association in cluster analysis with “tumor microenvironment” and “drug delivery” reflects a strategic paradigm shift to overcome limitations like poor targeting and tumor hypoxia (64).

This convergence is exemplified by research focused on engineering sophisticated nanoplatforms. Innovations include using nanocarriers like human serum albumin (HSA) to improve photosensitizer delivery (65), and designing oxygen-generating (e.g., HSA-MnO2) (66) or multimodal nanoparticles that combine PDT with therapies like chemodynamic therapy (e.g., Fe3O4@Chl) (67) or chemotherapy (68). A key advancement is the strategic enhancement of PDT’s immunogenic potential. This is achieved by developing organelle-targeting photosensitizers that concentrate ROS production in the endoplasmic reticulum to amplify ICD (69), and by creating bio-hybrid systems such as drug-loaded live BCG bacteria, which synergize chemotherapy with immunotherapy (70).

Consequently, the research frontier has decisively expanded to investigate PDT as a potent immune primer. Seminal work demonstrates that PDT-induced ICD, when combined with immune checkpoint inhibitors (e.g., anti-PD-1), can achieve profound tumor regression and inhibit metastasis by reshaping the immunosuppressive TME and promoting cytotoxic T-cell infiltration (68,71). This rationale extends to combining PDT-nanoplatforms with novel forms of regulated cell death [e.g., ferroptosis (67,72), cuproptosis (73)] to further amplify anti-tumor immunity. The frontier is further defined by “smart” nanoplatforms that actively reprogram the TME, such as those delivering immunomodulators like R848 (74), or those designed for nuclear targeting to activate the cGAS-STING pathway, thereby bridging PDT-induced damage with potent innate immune activation (75). The exploration of these multimodal combinations represents the current, intense focal point aimed at moving beyond monotherapy towards intelligent, system-based treatment strategies (76).

Future perspectives and challenges informed by bibliometric trends

Synthesizing these bibliometric observations, the future trajectory of PDT in BC is unequivocally pointed towards multimodal, technology-integrated therapies. However, the translation of these promising “hotspots” from robust preclinical models, as seen in the cited studies (67-71), to standardized clinical applications faces significant hurdles. Key challenges mirror the complexity of the strategies themselves: a lack of standardized protocols for photosensitizer and light dosing (10,52), incomplete understanding of the heterogeneous immune responses triggered (67,69), and concerns regarding the long-term biosafety and immunogenicity of nanomaterials (69,77). Crucially, optimal clinical parameters (dosage, timing, patient selection) for nano-PDT-immunotherapy combinations remain undefined, and the field suffers from a paucity of large-scale, multicenter randomized controlled trials (67,69).

Therefore, future research must pivot from demonstrating efficacy in models to addressing these translational bottlenecks. Efforts should focus on elucidating predictive biomarkers, establishing safety and dosing standards for novel nanoplatforms, and initiating rigorous clinical trials. Ultimately, progress will depend on fostering the enhanced international and interdisciplinary collaboration that our network analysis suggests is currently limited, enabling the field to fully harness the synergistic potential of PDT within the next generation of combination therapies for BC.

Advantages and limitations

Advantages

This study offers a comprehensive, data-driven overview of the PDT in BC research landscape over the past two decades. By employing multiple bibliometric techniques (e.g., co-authorship, co-citation, keyword co-occurrence, and burst detection), it moves beyond traditional reviews to objectively map the field’s intellectual structure, core themes, and dynamic evolution. The analysis not only identifies established knowledge bases but also clearly delineates the convergent frontier of nanotechnology and immunotherapy, providing a validated, quantitative foundation for understanding past progress and future directions.

Limitations and future methodological considerations

While bibliometric analysis provides powerful macro-level insights, several inherent methodological limitations must be acknowledged to objectively interpret our findings.

First, the analysis relies exclusively on English-language literature from the WoSCC database. This introduces a potential language and database bias, possibly underrepresenting significant research published in other languages or indexed in regional databases (e.g., CNKI), which may affect the completeness of the collaborative network and thematic analysis.

Second, bibliometric indicators have an inherent time lag in identifying “hot” topics. The reliance on publication and citation metrics means truly nascent, groundbreaking ideas may not be immediately visible until they accumulate sufficient publications. Our “frontiers” are thus validated, emerging trends rather than predictions of the very latest, unpublished research directions.

Third, while we identified limited international collaboration as a potential bottleneck, especially in complex interdisciplinary frontiers, other factors could influence research output and impact. These include variations in national research funding priorities, clinical trial regulations, and access to technological resources, which are not captured by publication data alone but can significantly shape the global research landscape.

Conclusions

This study systematically analyzed research advances in PDT for BC from 2000 to 2025 using bibliometric methods. Based on data from the WoSCC database, this study used visualization tools such as VOSviewer and CiteSpace to reveal the development trends, international cooperation networks, and core research themes in this field. The analysis showed that China and the United States were the countries with the highest number of publications in this area, but cooperation and communication among various countries and institutions remain limited in terms of quantity and depth. The keyword co-occurrence analysis highlighted core themes such as “HYP”, “5-aminolevulinic acid”, “protoporphyrin IX”, “nanoparticles”, and “immunotherapy”, reflecting a shift in research focus from basic mechanistic exploration to the optimization of new photosensitizers, clinical applications, and innovative treatment strategies. Additionally, the bivariate co-occurrence analysis of journals and bibliometric burst detection identified emerging research directions, including nanotechnology-enhanced PDT and combination immunotherapy with PDT. Overall, this study comprehensively mapped the knowledge landscape of PDT in BC, providing an important reference for scholars to understand disciplinary dynamics and plan future research directions.

Acknowledgments

We thank all authors who participated in the study of photodynamic therapy in bladder cancer.

Footnote

Reporting Checklist: The authors have completed the BIBLIO reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-1-0122/rc

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-1-0122/prf

Funding: This work was supported by Tianjin Key Medical Discipline (Specialty) Construction Project (No. TJYXZDXK-3-024C).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2026-1-0122/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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(English Language Editor: L. Huleatt)