Nasopharyngeal carcinoma (NPC) is an Epstein-Barr virus (EBV)-related cancer that is particularly prevalent in South East Asia and Southern China (1). Unlike other head and neck cancers, NPC is susceptible to radiotherapy (RT), which has become the mainstay of treatment for this disease. Despite advances in RT techniques and optimization of chemotherapy regimens, about 20% of patients with locally advanced NPC (LANPC) will recur (2). Moreover, recurrent and/or metastatic (R/M) NPC remains the most serious challenge because the median overall survival (OS) of these patients is only 15.7 months (3). Current conventional treatments, including RT, chemotherapy and surgery, are often accompanied by serious adverse effects and limited efficacy (4). Therefore, there is an urgent need for novel treatment strategies to improve the prognosis of patients with NPC.

In recent years, immunotherapy has sparked a revolution in the clinical management of cancer (5, 6). NPC is regarded as a typical “immune-hot” tumor due to the expression of EBV antigen and CD4⁺/CD8⁺ T-cell target proteins (7, 8), massive lymphocytic infiltration (9), the expression of programmed death ligand-1 (PD-L1) up to 89-95% (10), and the presence of several key immune molecules (CD40, CD70, CD80, and CD86) that regulate T-cell activation (11). Several clinical studies on NPC immunotherapy have shown early successes (12–14). Nevertheless, aside from individual reports, the overall characteristics of NPC immunotherapy clinical trials and whether contemporary studies are of sufficient quality to demonstrate the therapeutic value of immunotherapy in personalized NPC practice are unclear.

ClinicalTrials.gov, a publicly available registry and results database for human clinical studies, provides the most comprehensive clinical study information worldwide. In 2004, the International Committee of Medical Journal Editors (ICMJE) announced a policy as a prerequisite for publication that requires the registration of clinical trials before enrolling participants (15, 16). As of Nov 20, 2022, ClinicalTrials.gov contains detailed information on more than 430 000 clinical trials conducted in over 200 countries. ClinicalTrials.gov is recognized as a promising information source for facilitating the systematic evaluation of clinical trials (16).

In this study, we examined all of the interventional NPC studies registered on ClinicalTrials.gov in 15 years (Jan 1, 2008-Nov 20, 2022). We compared the fundamental characteristics of NPC trials focusing on immunotherapy with the characteristics of other non-immunotherapy NPC trials, and we evaluated the changes over time.

Well-designed clinical trials are desperately needed to validate the clinical applications of immunotherapy in NPC, given its promising efficacy. However, with an overall low incidence rate worldwide for its unique epidemiology, NPC does not attract much attention from most research. To the best of our knowledge, this is the first study assessing the critical characteristics of NPC immunotherapy trials over a 15-year period. By evaluating a comprehensive landscape, we found that NPC immunotherapy trials were predominantly phase 1-2 trials of limited sample size and tended to be single-arm, non-randomized and industry-funded. Blinding was rarely used. Asia was the major study location and clinical trials with international collaboration were lacking as well. The number of NPC immunotherapy trials increased exponentially after 2017, attributed to the exploration of ICIs. But the progress in trial design over time was slow and the basic trial characteristics largely remained unchanged. These findings raise concerns that trials evaluating the therapeutic role of immunotherapy in NPC may not be received the attention or efforts necessary to generate high-quality data. As a result, this orientation toward a less robust design may compromise evidence-based care for NPC.

As an EBV-associated malignancy, NPC is frequently infiltrated with varied stromal cells, making its microenvironment a highly heterogeneous and suppressive harbor that protects NPC cells from drug penetration and immune attack and promotes tumor progression (22, 23). This general immune landscape of NPC renders patients suitable for immunotherapy. In the past 15 years, immunotherapy trials accounted for 36.6% of all NPC trials. Unfortunately, 82.6% of NPC immunotherapy trials were phase 1-2 studies and tended to be single-arm, non-randomized, and enrolled less than 50 participants. Actually, the high proportion of single-arm, non-randomized, early-phase studies may either be because these studies are exploratory, hypotheses generating to fuel future randomized trials involving more patients, or because they were studying more highly innovative expensive cellular-based studies where funding was often inadequate for larger studies with more patients. In addition, the well-defined geographic distribution of NPC might further limit clinicians from conducting large-scale immunotherapy trials. Similarly, Xu et al. (24) tracked the evolving landscape of global immuno-oncology trials in 2007-2019 and found that most immunotherapy trials worldwide were phase 2 studies. Fortunately, NPC immunotherapy trials in 2018-2022 were more likely to be phase 2-3 (78.0% vs. 44.7%, P < 0.001) and had a sample size of more than 100 patients (42.3% vs. 24.3%, P = 0.055) than in 2008-2017. However, the other basic trial characteristics did not improve in an obvious manner over time.

Establishing international collaborative groups to foster research networks is an effective way to enroll more participants and improve the power of a study. However, 90.7% of NPC immunotherapy trials were conducted in only one region without sufficient international collaboration. Furthermore, in contrast to the findings that the US leads global immunotherapy research with stable growth (24), Asia (82.6%) is the major study location for NPC immunotherapy trials. And the proportion of US/Canada-centric decreased from 42.1% to 13.0% (P < 0.001) while the proportion of Asia-centric increased from 57.9% to 90.2% (P < 0.001) over the two periods. It’s not surprising because the Asian centricity is concordant with the unique epidemiology of NPC as a predominantly Asian disease. The patterns of NPC (incidence, histology) are different in South East Asia and the rest of the world. It would be helpful if clinical trials could address this discrepancy in future study designs.

Generally, the lengthy duration and high cost of immunotherapy trials may suppress industry enthusiasm. However, our findings showed that NPC immunotherapy trials were more likely to be industry-funded compared with other NPC trials (34.2% vs. 11.5%, P < 0.001) and the proportion has increased over time (21.1% vs. 38.2%, P = 0.077). It indicates a large market potential in the field of NPC immunotherapy, thus raising financial interests and industrial enthusiasm for sponsorship of such trials. Moreover, 60.2% of NPC immunotherapy trials were other-funded, and this proportion has remained stable over time. It implies that academic institutions and governments continue to play an important role in supporting immunotherapy clinical research for NPC and shoulder vital public health responsibility. Still, allocating more resources to NPC immunotherapy from all relevant parties is essential to improve the effective leveraging of the constrained resources.

It is noteworthy that there was an increasing number of NPC immunotherapy trials after 2017. Actually, this reflects more recent successes in other major tumor types, and therefore there is an increasing interest in studying this intervention in an EBV-related tumor type like NPC that does not have many mutational targets. However, only the number of ICI trials increased significantly, while the numbers of ACT, vaccine and immunomodulator trials remained stagnant. A potential explanation is that ICIs as pan-cancerous antitumor agents were found to have equally promising efficacy in NPC, thus spurring enthusiasm for research. Furthermore, the recognition of ICI-based immunotherapy by the 2018 Nobel Prize in Physiology or Medicine might have further increased researchers’ interest in the exploration of ICIs in NPC. In contrast, the exploration and further application of EBV-specific ACTs and vaccines and immunomodulators were hampered by the lack of specific and effective targets, generally low and transient immune responses, technical limitations and financial shortages. According to the results of published NPC studies (Supplementary Table 1), ICIs monotherapy achieves 17.1-34.0% of the objective response rate in the second or later-line treatment of R/M NPC (14, 25–30). In the first-line treatment, the addition of ICIs to chemotherapy also significantly improved progression-free survival and OS in R/M NPC (31–33). Further studies are needed to assess the therapeutic value of ICIs in LANPC and early-stage disease. Notably, CAR-T/TCR-T cell therapy and antibody-drug conjugates may be another promising immunotherapy modality for NPC, as they have shown promising efficacy in a variety of other cancers (34, 35). Therefore, concerted efforts by oncologists, sponsors and other concerned parties are still needed to advance the development of immunotherapy for NPC.

Integration with conventional treatment modalities is one of the trends in immunotherapy. In this study, we found that the most commonly investigated immunotherapy regimen in NPC was combination chemotherapy, followed by combination radiochemotherapy. A recently published study reported on the promising antitumor activity and a manageable toxicity profile of immunotherapy combined with antiangiogenic therapy in R/M NPC (36). In addition, future NPC studies could consider more novel combination strategies to enhance the clinical responses, for example, ICIs combined with ACT (37) or CAR-T cell therapy combined with the oncolytic virus (38).

Limitations of this study should also be acknowledged. First, not all investigators choose ClinicalTrials.gov to register their projects. There are many alternative registries available around the world (39). Nevertheless, ClinicalTrials.gov is the most robust database to date, accounting for 70–80% of the unique clinical trials recorded by the World Health Organization (39). Second, partial NPC trials have not yet been registered on ClinicalTrials.gov, which hindered us from more fully reflecting current global trends in NPC immunotherapy trials. Third, the National Library of Medicine, which operates ClinicalTrials.gov, is unable to validate all registered data. The accuracy of the data relies on the study sponsor. Fourth, we did not include noninterventional trials in our analysis.

In conclusion, NPC Immunotherapy trials over a 15-year period have been largely exploratory. Advancing the clinical application of immunotherapy in NPC requires more attention and concerted efforts to improve the quality of trials.

Publicly available datasets were analyzed in this study. This data can be found here: https://clinicaltrials.gov/.

TL had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. HGH, YY, and XD contributed equally to this work. Concept and design: HGH, YY, XD, HH, and TL. Acquisition, analysis, or interpretation of data: HGH, YY, XD, and TL. Drafting of the manuscript: HGH, YY, and XD. Critical revision of the manuscript for important intellectual content: All authors. Statistical analysis: HGH and XD. Obtained funding: HH and TL. Administrative, technical, or material support: HH and TL. Supervision: HH and TL. All authors contributed to the article and approved the submitted version.