City of Hope Research Identifies Physical Organ Enlargement as Primary Driver Linking Obesity to Elevated Cancer Risk

City of Hope scientists find that obesity causes organs to grow more cells, creating a "lottery" effect that increases the likelihood of cancer mutations.

By: AXL Media

Published: Mar 27, 2026, 7:23 AM EDT

Source: Information for this report was sourced from City of Hope

A Mechanical Explanation for the Biological Link Between Weight and Malignancy

The long established correlation between obesity and cancer has traditionally been attributed to metabolic shifts or hormonal imbalances, but new research from City of Hope and TGen suggests a more direct, physical cause. Scientists have identified that as a body gains excess weight, internal organs expand to meet the heightened energy demands of a larger frame. This growth is not merely a swelling of existing tissue but a systematic increase in the total number of cells within the organ. By fundamentally changing the scale of the organ, the body inadvertently increases the statistical probability of a genetic error occurring during the process of cellular replication.

Quantifying the Scale of Organ Expansion Across the BMI Spectrum

Led by Dr. Cristian Tomasetti, the research team utilized CT scans to evaluate 747 adults representing the full spectrum of Body Mass Index, from underweight to severely obese. The investigation focused on the liver, kidneys, and pancreas, revealing a consistent trend of enlargement as body mass increased. Specifically, researchers noted that for every five point rise in a patient's BMI, the liver grew by 12%, while the kidneys and pancreas expanded by 9% and 7% respectively. This study marks the first time that multiple organ dimensions have been mapped across such a broad demographic, providing a concrete link between external weight gain and internal structural changes.

The Shift from Fatter Cells to Increased Cellular Population

A critical finding of the study corrects previous assumptions that larger organs in obese individuals were primarily the result of hypertrophy, or individual cells growing larger. By analyzing kidney tissue from autopsies and biopsies, the lab demonstrated that over 60% of organ growth is actually driven by hyperplasia, the creation of entirely new cells. This distinction is vital for cancer research because fatter cells do not necessarily increase mutation risk, whereas a higher volume of dividing cells creates a larger "lottery" of potential genetic mishaps. According to Dr. Tomasetti, every additional cell represents a new chance for a mutation to take hold and evolve into a malignancy.