Breast cancer remained the world’s most studied disease for the fifth consecutive year in 2025, according to a new annual analysis from clinical data analytics company Phesi.

The findings are based on an analysis of 65,892 recruiting clinical trials captured within Phesi’s AI-driven Trial Accelerator platform. The report shows that breast cancer across all subtypes, including triple negative disease and PIK3CA-mutated cancer, continues to dominate global clinical research activity.

The top five most studied diseases in 2025 were breast cancer, solid tumours, stroke, prostate cancer and non-small cell lung cancer. Obesity ranked sixth, narrowly missing the top five, but is expected to rise further as GLP-1-related research expands.

In addition to disease focus, the report highlights a modest improvement in clinical trial attrition rates. While still elevated, the proportion of Phase 2 trials terminated early fell to 26%, marking a four-year low. This compares with 31% in 2024, 29% in 2023 and around 20% before Covid-19.

Phesi founder and president Dr Gen Li said: “While it is positive to see trial attrition rates fall, a quarter of Phase 2 trials ending early is still unacceptably high.”

Li said sponsors continue to face pressure from macroeconomic constraints, pricing challenges and increased competition in global trial activity, particularly in Asia. He added that renewed regulatory focus on country-level representation, including from the FDA, is also shaping site selection strategies.

“ Well-known and high-profile investigator sites are quickly saturated as sponsors seek them out. However, there is considerable opportunity to identify investigator sites elsewhere that may have a shorter clinical trial and enrolment history, but have capacity and have delivered high quality data in previous trials,” Li said.

At a country level, the United States continued to lead global clinical trial activity in 2025, hosting the highest number of recruiting investigator sites overall and across all five of the most studied diseases. China ranked second for four of the five indications, with Canada taking second place for prostate cancer trials.

China also recorded the fastest growth in recruiting investigator sites between 2023 and 2025, increasing by 51%, compared with 42% growth in the United States. France, Italy and Spain completed the top five countries globally.

Phesi said the increasing complexity of the clinical development landscape makes data-driven decision-making essential. “The increase in competition, regulatory changes and acceptance of digital patient data mean it is vital for sponsors to be led by insight informed by big data and AI, rather than instinct,” Li added.

The report also points to obesity as a disease area to watch. A separate Phesi analysis published in September 2025 found more than 100 diseases are now being investigated in connection with GLP-1 use. This growing body of research reflects rising interest in obesity as a comorbidity and suggests it could enter the top five most studied diseases within the next one to two years.

Rising GLP-1 usage is also expected to influence clinical trial design across multiple therapy areas, as weight loss may affect dosing, endpoints and study parameters.

“Breast cancer continues to dominate because researchers have a far deeper understanding of its biomarkers,” Li said. “Although the pandemic is still having lingering effects as a disruptor, sponsors should now be looking ahead to what the next disruptor might be.”

Phesi has published annual reports on the world’s most studied diseases since 2021. Its Trial Accelerator platform is described by the company as the world’s largest contextualised clinical trial database and underpins ongoing analyses of global clinical development trends.