Highlights

Phoenix-based biomedical research institute TGen and its parent organization City of Hope published research Tuesday identifying a cellular mechanism that explains why excess body weight raises cancer risk — a question scientists have long been unable to answer with precision.

The study, released March 24 in Cancer Research, a journal of the American Association for Cancer Research, found that as a person gains weight, organs grow larger by accumulating more cells to meet the energy demands of a bigger body. More cells mean more opportunities for DNA copying errors during cell division, increasing the probability that one cell will develop into a malignancy.

"People have long been told that obesity increases cancer risk, but they are rarely told why," said senior author Cristian Tomasetti, Ph.D., director of City of Hope's Center for Cancer Prevention, Early Detection and Monitoring and a professor in the Early Detection and Prevention Division at TGen. "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."

The research team conducted a two-part study. In the first phase, researchers used CT scans to measure the liver, kidneys, and pancreas of 747 adults whose body mass index ranged from underweight (18.5 BMI) to severely obese (40-plus BMI). The team found that for every 5-point increase in BMI, the liver grew by 12%, kidneys by 9%, and the pancreas by 7%.

In the second phase, researchers counted cells in kidney tissue from autopsies and reanalyzed biopsy data from living patients. They found that more than 60% of kidney growth resulted from an increase in cell count — a process called hyperplasia — rather than from individual cells growing larger, a process called hypertrophy. The finding directly contradicts earlier theories that attributed organ enlargement in obese individuals primarily to enlarged fat cells.

Tomasetti framed the risk in probabilistic terms. "Think of playing the lottery: The more tickets you buy, the greater your chances of winning," he said. "Similarly, the more cells in an organ, the more mutations and the greater the risk of one cell going aw[ry]."

The study also proposes that organ size may offer a more accurate measure of obesity-related cancer risk than BMI, and the authors say the findings underscore the importance of maintaining a healthy weight beginning in early childhood. The release notes this is the first study to analyze the size of multiple organs across a large cohort spanning the full BMI spectrum.

TGen, a nonprofit research institute, operates as part of City of Hope, which the release describes as one of the largest 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.

Sources

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  1. tgen.org retrieved 2026-05-02T08:57:39.899345+00:00

Authored by Claude, drafted from primary-source material with beat-specific editorial guides at The Scottsdale Signal. Sources retrieved at 2026-05-02T08:57:39.899345+00:00. Every claim traces to a source. Reviewed before publish under our five-gate editorial process.