COVID inflammation – As Omicron-era cases flooded hospitals in 2022, researchers studying mice with dormant breast cancer cells found viral infections could make tumors return—then saw similar patterns in human records. The work, published in Nature, points to inflammation signals
In early 2022. when Omicron was beginning to drive another sharp surge of COVID-19 cases. researchers at James DeGregori’s University of Colorado Anschutz lab noticed something that didn’t fit the usual expectations. Lab mice carrying dormant breast cancer cells were infected with either influenza or SARS-CoV-2—and the animals were significantly more likely to develop aggressive lung tumors.
What happens in a mouse doesn’t automatically map onto a person. Still, when the team examined healthcare databases, they were surprised to find something similar showing up in the human population.
Analyses of records from the U.K. Biobank found that cancer survivors who contracted COVID in 2020—when the virus was new and no vaccine was available—were significantly more likely to die of recurring cancer than patients who did not get infected. The relationship was especially pronounced within the year after the COVID infection. In a separate U.S. breast cancer database. breast cancer patients in remission who got COVID were significantly more likely to develop metastatic lung tumors than patients who did not contract the virus.
The researchers couldn’t analyze influenza’s effects as thoroughly. Most flu infections don’t make it into medical charts because many patients recover at home without care. And their approach also meant they couldn’t determine whether the severity of a patient’s COVID infection influenced the likelihood of cancer recurrence. Even so. the timing and novelty of COVID gave the team a rare kind of data—enough to track how viral inflammation might affect dormant cancer over time. Their findings were published last year in the journal Nature.
When DeGregori talked about recurrence, his warning sounded blunt. “When [cancer] comes back, it comes back with a fury,” he said. “We think that these virus infections can be almost like fuel for the fire.”
The scale of the pandemic changed what scientists could study.
The sheer number of people infected by COVID has offered researchers a “critical mass of data” that would be difficult to obtain in ordinary times. said Dr. Stanley Perlman, a University of Iowa microbiologist who studies coronaviruses. In a global pandemic, he said, “where the whole population gets infected, basically you have a denominator of 7 billion people.”.
As years of post-pandemic data piled up, scientists also gained a sharper view of post-viral illness. The rapid rise of long COVID helped supercharge research on post-viral syndromes—an umbrella of lingering symptoms doctors have observed in some patients after pneumonia. flu. and other viral infections. That broader effort is now feeding into another question: how viruses might shape cancer behavior long after the initial infection passes.
“This is something that merits more attention,” said Dr. Aditya Bardia, director of Translational Research Integration at the UCLA Health Jonsson Comprehensive Cancer Center. Bardia’s lab has also observed associations between COVID infection and breast cancer recurrence. though that work has not yet been submitted for peer review.
Even with those signals, many researchers say it’s still too early to call COVID a cancer-causing virus.
There isn’t sufficient evidence to indicate that COVID is an oncogenic. or cancer-causing. virus. a half-dozen researchers contacted for this article said. Structurally. the virus differs from known oncogenic viruses such as human papilloma virus. linked to cervical cancer. and hepatitis B and C. associated with liver cancer.
Still, the pandemic produced evidence that viral infection may play a role in reawakening dormant cancer cells that already exist in a patient’s body.
Dr. Patrick Moore. a virologist and epidemiologist at the University of Pittsburgh. described it this way: “COVID and influenza do not cause cancer under themselves. but if you have cancer and you have dormant cancer cells that are normally under control by your immune system. getting a severe case of COVID can help reactivate those existing cancers.”.
At the same time, the pandemic era itself complicated what researchers could see. A sharp increase in metastatic breast cancer cases in the early years of COVID was largely attributed to care delayed by pandemic restrictions—not to a true rise in incidence. More recent work, however, suggests the association may not be just a logistics problem.
“It’s not just the logistics of the pandemic. but it’s really something inherent to infection” behind the association with cancer recurrence. said Melanie Ott. director of the Gladstone Institute of Virology and a professor of medicine at UC San Francisco. Ott pointed out the effect isn’t specific to COVID. DeGregori’s Nature paper showed influenza could trigger the same pattern.
One immune mechanism ties those findings together. One of the body’s natural defense responses to viruses like COVID or influenza is the release of cytokines—proteins that act as chemical messengers to coordinate the immune system’s response. But in some cases of severe infection, the immune system can “overcorrect,” releasing an excess amount of these proteins. That dangerous overshoot is called a cytokine storm.
Early in the pandemic. researchers found that patients with severe COVID who died or required hospitalization were much more likely to have runaway levels of cytokines. including a particular protein called interleukin-6. or IL-6. And chronically high IL-6 levels have been linked to recurrence and metastasis of multiple types of cancer.
DeGregori’s team connected the human pattern to a biological pathway in animals. They found that breast cancer cells in mice whose dormant cancers returned after a COVID infection reactivated in response to high levels of IL-6. Still, their work couldn’t prove the same biological process happens in humans, DeGregori said. The human data—showing a high correlation between COVID infection and cancer recurrence—is what makes him believe the underlying mechanism might be real.
But not everyone reads the numbers the same way.
Dr. Doug Wallace. director of the Center for Mitochondrial and Epigenomic Medicine at Children’s Hospital of Philadelphia and a co-author on the Nature paper. said he has a “slightly different interpretation” of the data. Wallace also pointed out that IL-6 inhibits mitochondria, the parts of a cell that generate energy. He thinks the suppression of the cell’s powerhouses may be what encourages cancer growth.
Wallace added that other viruses shut down mitochondrial function too. He said SARS-CoV-2 seems particularly good at it—an ability that could help explain why some people experience the lingering misery of long COVID, and why others might see unexpected cancer recurrence.
The debate is still unsettled, and researchers stressed that the field remains in its early days. There is no definitive causal link yet between COVID infection and cancer recurrence.
Dr. Eric Winer, director of the Yale Cancer Center, put it sharply. “It’s fair to say that [COVID infection] could be added to the long list of theoretical reasons that cancer might be more likely to come back. [but] I’m on the skeptical side of all things. Prove it to me,” he said. “This is one where I’d say, interesting finding, let’s look more.”.
For now, the evidence suggests the question itself is worth pursuing—especially for patients whose immune systems are already vulnerable.
Moore said the most practical takeaway is about avoiding severe viral infections in general. “There’s a very. very. very compelling reason for those patients who have chronic diseases to avoid getting a severe case of influenza or COVID or respiratory syncytial [virus] — all of these diseases for which good. safe. effective vaccines exist. ” he said.
COVID cancer recurrence IL-6 cytokine storm breast cancer long COVID SARS-CoV-2 influenza U.K. Biobank Nature