Study Links Obesity to Increased Cancer Risk Through Organ Growth

City of Hope and TGen researchers discover a key mechanism behind obesity's connection to cancer development.

Mar. 27, 2026 at 10:44am

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Scientists at City of Hope and TGen have published a study in Cancer Research that reveals a major driving force behind how obesity increases cancer risk across multiple organs. The research shows that as a person gains weight, their organs also grow in size by accumulating more cells, boosting the odds of DNA errors and cancer development. The study is the first to analyze the size of the liver, kidneys, and pancreas in a large cohort of individuals across the full BMI spectrum, finding that organ size increases significantly with higher BMI.

Why it matters

This study provides important insights into the biological mechanisms linking obesity to cancer risk. By understanding that excess weight doesn't just affect metabolism or hormones, but can physically enlarge organs and increase the number of cells at risk for cancer, it emphasizes the importance of maintaining a healthy weight from an early age to reduce long-term cancer susceptibility.

The details

The researchers conducted a two-part study. First, they evaluated 747 adults spanning the full BMI spectrum and used CT scans to measure the size of their liver, kidneys, and pancreas. They found that for every 5-point increase in BMI, the liver grew by 12%, kidneys by 9%, and the pancreas by 7%. Next, the team analyzed kidney tissue samples and found that over 60% of the organ growth was due to an increase in the number of cells, rather than just individual cells growing larger. This increase in cell count raises the odds of DNA errors and uncontrolled cell growth leading to cancer.

  • The study was published on March 27, 2026 in the journal Cancer Research.

The players

Cristian Tomasetti

The senior author of the study, director of City of Hope's Center for Cancer Prevention, Early Detection and Monitoring, and professor in the Early Detection and Prevention Division at TGen.

Sophie Pénisson

The first author of the study, an associate professor at TGen.

City of Hope

One of the largest and most advanced cancer research and treatment organizations in the United States, with its National Medical Center ranked among the nation's top cancer centers by U.S. News & World Report.

TGen

The Translational Genomics Research Institute, part of City of Hope, that collaborated on the study.

Debbie C. Thurmond

The director of the Arthur Riggs Diabetes & Metabolism Research Institute and Chan Soon-Shiong Shapiro Distinguished Chair in Diabetes at City of Hope.

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What they’re saying

“People have long been told that obesity increases cancer risk, but they are rarely told why. Our study reveals that excess weight doesn't just affect metabolism or hormones — it can physically enlarge organs, creating more opportunities for cancer to take hold. Understanding that process matters because it helps explain how everyday health choices can shape cancer risk years for even decades down the line.”

— Cristian Tomasetti, Director of City of Hope's Center for Cancer Prevention, Early Detection and Monitoring and professor in the Early Detection and Prevention Division at TGen

“When an organ doubles in size, it is expected to roughly double its risk of developing cancer. BMI is a poor proxy for telling us what the size of an organ is, as BMI doesn't distinguish between fat and lean tissue. Our work suggests that, at least for some organs, their dimensions may predict cancer risk better than BMI.”

— Sophie Pénisson, Associate professor at TGen

“This exciting research deepens our understanding of how obesity may lead to cancer and highlights the role of organ growth in this process, which is also relevant for many individuals with diabetes. It will be important to see if the new anti-obesity drugs can revert this process for cancer prevention.”

— Debbie C. Thurmond, Director of the Arthur Riggs Diabetes & Metabolism Research Institute and Chan Soon-Shiong Shapiro Distinguished Chair in Diabetes at City of Hope

What’s next

Future studies will explore whether losing weight can reduce organ size and cancer risk, and the potential effect of GLP-1 drugs on lowering cancer risk through weight loss.

The takeaway

This study provides a key mechanism to explain the link between obesity and increased cancer risk, highlighting the importance of maintaining a healthy weight from a young age to reduce the long-term accumulation of cell mutations and cancer development.