Researchers at City of Hope and TGen have identified a biological mechanism that explains how obesity increases cancer risk across multiple organs, according to a recently published study.
The research shows that excess body weight causes organs to enlarge through a process called hyperplasia, or an increase in the number of cells. This expansion increases the likelihood of mutations that can lead to malignancy. The findings, published in the journal Cancer Research, provide one of the clearest biological explanations yet for the established link between obesity and at least 13 types of cancer.
Scientists at City of Hope and its Translational Genomics Research Institute, known as TGen, analyzed organ size data and found that larger bodies develop larger organs with more cells to meet higher energy demands.
The study found a strong positive correlation between body mass index and the volume of organs such as the liver, pancreas, and kidneys in 747 adults. In the kidneys, for example, more than 60% of the growth resulted from hyperplasia.
Cristian Tomasetti, Ph.D., senior author and 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, said the mechanism is straightforward math. “People have long been told that obesity increases cancer risk, but they are rarely told why,” he stated. “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.”
Tomasetti added, “Understanding that process matters because it helps explain how everyday health choices can shape cancer risk years or even decades down the line.” He noted there are other ways obesity promotes cancer, “but this is a major mechanism.”
The study builds on decades of epidemiological data showing that overweight and obesity are linked to higher rates of breast, colon, endometrial, kidney, liver, and other cancers. Researchers emphasized that the work supports the importance of maintaining a healthy weight from early childhood and suggested organ size could offer a more precise risk predictor than body mass index alone.
The paper, titled “Hyperplasia Functions as a Link Between Obesity and Cancer,” was supported by the John Templeton Foundation, the Lustgarten Foundation for Pancreatic Cancer Research, the Maryland Cigarette Restitution Fund and the National Institutes of Health. City of Hope and TGen described the findings as a first-of-its-kind explanation of the physical cellular pathway.
The research arrives as global obesity rates continue to climb and as new weight-management therapies draw attention for potential long-term health effects. Officials at the institutions said the results underscore prevention strategies focused on healthy weight across the lifespan.
