New Study Reveals How Obesity Drives Cancer Risk by Increasing Cell Numbers

Scientists at City of Hope and Translational Genomics Research Institute have identified a key biological mechanism explaining how obesity increases cancer risk. The study, published in Cancer Research, shows that excess body weight can physically enlarge organs, increasing the likelihood of cancer development.

According to senior author Cristian Tomasetti, obesity does more than alter metabolism or hormones—it drives organ growth by increasing the number of cells. As body weight rises, organs such as the liver, kidneys, and pancreas expand to meet higher energy demands. This growth occurs mainly through hyperplasia (an increase in cell number), rather than just enlargement of existing cells.

To investigate, researchers analyzed 747 adults across a wide body mass index (BMI) range using CT scans. They found that for every 5-point increase in BMI, the liver enlarged by 12%, kidneys by 9%, and pancreas by 7%. Further tissue analysis revealed that over 60% of kidney growth was due to an increase in cell, confirming that obesity significantly raises the number of cells within organs.

This increase in cell count is critical because cancer often arises from DNA errors during cell division. With more cells present, the probability of mutations rises—similar to increasing chances in a lottery. The study confirmed a strong link between enlarged organ size and higher cancer risk.

Importantly, the findings suggest that BMI alone may not accurately predict cancer risk, as it does not reflect organ size or composition. Researchers emphasize maintaining a healthy weight from early life, as prolonged obesity allows more time for harmful mutations to accumulate, increasing long-term cancer risk.

REFERENCE: Sophie Pénisson, Maren Weischer, Lu Li, Yifan Zhang, Haley Grant, Ruihan L. Yuan, Kevin M. Arnold, Mete Mülazımoğlu, Yan Wang, Satomi Kawamoto, Daniel Fadaei. Fouladi, Shahab Shayesteh, Alejandra Blanco, Saeed Ghandili, Eva Zinreich, Jefferson S. Graves, Syed Rahmanuddin, Scott E. Kern, Pei-Hsun Wu, Jody E. Hooper, Alan Yuille, Elliot K. Fishman, Linda Chu, Cristian Tomasetti; Hyperplasia Functions as a Link Between Obesity and Cancer. Cancer Res 2026; https://doi.org/10.1158/0008-5472.CAN-25-2487