Cancer most frequently spreads to the liver; here’s why

Penn researchers show hepatocytes orchestrate the ‘seed and soil’ process for cancer spread to the liver

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Credit: Penn Medicine

PHILADELPHIA – When cancer spreads to another organ, it most commonly moves to the liver, and now researchers at the Abramson Cancer Center of the University of Pennsylvania say they know why. A new study, published today in Nature, shows hepatocytes – the chief functional cells of the liver – are at the center of a chain reaction that makes it particularly susceptible to cancer cells. These hepatocytes respond to inflammation by activating a protein called STAT3, which in turn increases their production of other proteins called SAA, which then remodel the liver and create the “soil” needed for cancer cells to “seed.” The researchers show that stopping this process by using antibodies that block IL-6 – the inflammatory signal that drives this chain reaction – can limit the potential of cancer to spread to the liver.

“The seed-and-soil hypothesis is well-recognized, but our research now shows that hepatocytes are the major orchestrators of this process,” said senior author Gregory L. Beatty, MD, PhD, an assistant professor of Hematology-Oncology at Penn’s Perelman School of Medicine. Jae W. Lee, an MD/PhD candidate in Beatty’s laboratory, is the lead author.

For this study, the team first used mouse models of pancreatic ductal adenocarcinoma (PDAC), the most common type of pancreatic cancer and currently the third leading cause of cancer death in the United States. They found that nearly all hepatocytes showed STAT3 activation in mice with cancer, compared to less than two percent of hepatocytes in mice without tumors. They then partnered with investigators at the Mayo Clinic Arizona and other Penn colleagues to show that this same biology could be seen in patients with pancreatic cancer as well colon and lung cancer. Genetically deleting STAT3 only in hepatocytes effectively blocked the increased susceptibility of the liver to cancer seeding in mice. The team collaborated further with investigators at the University of Kentucky to show that IL-6 controls STAT3 signaling in these cells and instructs hepatocytes to make SAA, which acts as an alarm to attract inflammatory cells and initiate a fibrotic reaction that together establish the “soil.”

“The liver is an important sensor in the body,” Lee said. “We show that hepatocytes sense inflammation and respond in a structured way that cancer uses to help it spread.”

The study also found that IL-6 drives changes in the liver whether there’s a tumor present or not, implying that any condition associated with increased IL-6 levels – such as obesity or cardiovascular disease, among others – could affect the liver’s receptiveness to cancer. Researchers say this provides evidence that therapies which target hepatocytes may be able to prevent cancer from spreading to the liver, a major cause of cancer mortality.

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This study was supported by the National Institutes of Health (F30 CA196106, T32 HL007439, T32 CA009140, R01 CA197916, R01 HL134731), the University of Pennsylvania Molecular Pathology and Imaging Core of the Center for Molecular Studies in Digestive and Liver Diseases (P30 DK050306), a Pancreatic Cancer Action Network-AACR Career Development Award (15-20-25-BEAT), a Stand Up To Cancer Innovative Research Grant (SU2C-AACR-IRG 13-17), a Research Support Grant from the University of Kentucky Office of the Vice President for Research, the American Surgical Association Foundation Fellowship, the Cooperative Tissue Health Network, the Mayo Clinic Arizona, the University of Pennsylvania Pancreatic Cancer Research Center, and the Abramson Cancer Center Translational Centers of Excellence.

Penn Medicine is one of the world’s leading academic medical centers, dedicated to the related missions of medical education, biomedical research, and excellence in patient care. Penn Medicine consists of the Raymond and Ruth Perelman School of Medicine at the University of Pennsylvania (founded in 1765 as the nation’s first medical school) and the University of Pennsylvania Health System, which together form a $7.8 billion enterprise.

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Related Journal Article

http://dx.doi.org/10.1038/s41586-019-1004-y

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