Common Threads Across the Most-Studied Diseases: Q&A with Gen Li

In a conversation with Pharmaceutical Executive, Phesi founder and CEO Gen Li discusses his company’s recent global analysis of clinical trials. While the report once again showed that breast cancer is the most studied disease, it also revealed several other surprising trends in clinical trials.

Pharmaceutical Executive: What do the top most-studied diseases in 2025 have in common?
Gen Li: A common thread across the most-studied diseases last year is the continued dominance of oncology. Cancer indications continue to account for a significant share of clinical trial activity because researchers have a far deeper understanding of cancer biomarkers. There are still many unmet needs to be addressed, such as in triple negative breast cancer, but sustained clinical research investment in oncology is encouraging.

PE: What caused Phase II trial attrition rates to drop to a four-year low?
Li: We’ve started to see some encouraging movement in Phase II attrition rates. The most recent attrition rate of 26% is the lowest in four years, after reaching 31% in 2024 and 29% in 2023. This suggests the industry is gradually finding its footing again following the disruption caused by COVID.

That said, while it’s positive to see rates fall, a quarter of Phase II trials ending early is still unacceptably high. That level of attrition inevitably has a knock-on effect on Phase III trials and a significant impact on companies’ return on investment.

Sponsors are still operating in a challenging environment, with macroeconomic constraints, pricing pressures and increased activity in regions such as China all shaping decision-making. At the same time, regulators such as the FDA are placing renewed emphasis on country-specific representation, which is contributing to saturated investigator sites.

PE: Why does the US continue to lead global clinical trial activity?
Li: The US hosts the largest number of recruiting clinical trial investigator sites overall and for each of the five most studied diseases. The US has always been highly competitive simply because of its size and the sheer volume of patients available.

Although, competition in the US isn’t evenly distributed. A relatively small group of well-known and high-profile investigator sites become quickly saturated, while newer or less prominent sites struggle for visibility, despite being just as capable of recruiting effectively.

That’s where clinical data science has a real role to play. By looking beyond reputation alone and using contextualized, real-world data to identify high-performing but under-recognized investigator sites, sponsors can select investigator sites with far greater precision and ease the bottlenecks that form around the biggest names.

PE: How does China’s growth compare to that of the US?
Li: Although the US still leads in the overall number of recruiting investigator sites, China is emerging as the fastest-growing market. China now ranks as second for all of the top five most-studied diseases except prostate cancer, where Canada takes second place.

What really stands out is the pace of growth. Between 2023 and 2025, China recorded the strongest growth in investigator site numbers, increasing by 51% compared with 42% for the US. Some of that momentum has been supported by international experience, including strong links with the US. Many researchers and clinicians trained in the US have returned to China, bringing that expertise with them and helping to build local trial infrastructure and capability.

PE: What trends do you expect to see in 2026 in recruiting trials?
Li: Obesity is one of the disease areas to watch most closely. It remained just outside the top five most studied diseases last year, ranking sixth. However, there is growing interest in obesity as a comorbidity in a wide range of diseases, with more than 100 diseases now being investigated in connection with GLP-1 use. This indicates that obesity will most likely enter the top five within the next one to two years.

More broadly, the rise in GLP-1 usage has the potential to reshape the clinical development landscape. Because obesity is an influential comorbidity, weight loss may alter study parameters, dosing and endpoints. Over time, wider use of GLP-1s will also shift the focus toward prevention and treating clusters of related disease.