Breast cancer tops list of most-studied diseases for fifth consecutive year, Phesi annual analysis finds

Phesi has released its annual report into the world’s most studied diseases, analyzing data from 65,892 recruiting clinical trials in its AI-driven Trial Accelerator™ platform. The findings show that breast cancer across all subtypes – from triple-negative to PIK3CA – remains the world’s most studied disease for the fifth year running. The top five was rounded out by solid tumors, stroke, prostate cancer and non-small cell lung cancer (NSCLC) (table 1). The report also showed a small improvement in trial attrition; however a quarter (26%) of trials are still terminated in Phase II.

Country-level analysis shows the United States continues to host the largest number of recruiting clinical trial investigator sites overall and for each of the five most studied diseases. China ranks second for all of the top five except prostate cancer, where Canada takes second place. China also recorded the strongest growth in investigator site numbers between 2023 and 2025, increasing by 51% compared with 42% for the US (fig.2). France, Italy and Spain complete the top five countries for recruiting investigator sites.

“While it is positive to see trial attrition rates fall, a quarter of Phase II trials ending early is still unacceptably high,” commented Dr Gen Li, founder and president of Phesi. “Sponsors remain under pressure from macroeconomic constraints, pricing challenges and increased activity in regions such as China. We are also seeing the effect of renewed emphasis from regulators, including the FDA, on country-specific representation. 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. 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. Considerable volumes of contextualized and real-world data exist to power clinical data analytics that overcome these hurdles.”

Phesi’s data confirms that the 26% Phase II termination rate is a four-year low, though still above pre-pandemic levels. In 2024, 31% of Phase II trials were terminated, up from 29% in 2023 and around 20% before Covid-19 (fig.1). Obesity remained just outside the top five most studied diseases, ranking sixth in 2025. A separate Phesi analysis in September 2025 showed that more than 100 diseases are being investigated in connection with GLP-1 use, reflecting growing interest in obesity as a comorbidity in a wide range of diseases. This increase indicates that obesity is the disease area most likely to enter the top five within the next one to two years. Rising GLP-1 usage will also influence clinical development in other fields, as obesity is an important comorbidity and weight loss may alter study parameters, dosing and endpoints.

“Breast cancer continues to dominate because researchers have a far deeper understanding of its biomarkers. There are still many unmet needs to be addressed, such as in triple negative breast cancer, but sustained clinical research investment in this devastating disease is encouraging,” continued Dr Li. “Although the pandemic is still having lingering effects as a disruptor, sponsors should now be looking ahead to what the next disruptor might be. The broader adoption of GLP-1s, for example, could reshape the clinical development landscape as the focus shifts towards prevention and treating clusters of related disease.”

Phesi has published annual reports on the world’s most studied diseases since 2021 and issues regular analyses on global clinical development. These reports draw on the award-winning Trial Accelerator platform, the world’s largest contextualized clinical trial database.

Phesi’s Digital Patient Profile catalog today holds 44 patient profiles across disease areas including oncology, respiratory, metabolic, dermatology, inflammation, CVS and CNS, and all of the top five most studied diseases, including:

• Breast cancer: PIK3CA, HER2-Positive
• NSCLC: general NSCLC and KRAS mutated G12C and G12D NSCLC, and NSCLC-EGFR
• Stroke: general and Acute Ischemic Stroke
• Prostate cancer: metastatic, Castration Resistant
• Pancreatic cancer: KRAS mutated, G12D
• Parkinson’s Disease: Deep Brain Stimulation
• Obesity-related indications: MASH, Alzheimer’s, Acute Coronary Syndrome (ACS), Osteoarthritis, GLP-1

To read the full report, visit: info.phesi.com/top-five-2025-studied-diseases