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By Hannah Millington
Health Reporter
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Respiratory infections like COVID-19 and the flu may increase the risk of dormant breast cancer cells reactivating and spreading in those with a history of the disease.
This is the conclusion of a study based on experiments with mice and observational human health data by researchers at the University of Colorado, the Montefiore Einstein Comprehensive Cancer Center (MECCC) in New York and Utrecht University.
Such an awakening, the team warn, could trigger new metastatic tumors.
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"Dormant cancer cells are like the embers left in an abandoned campfire—and respiratory viruses are like a strong wind that reignites the flames," said paper author James DeGregori of the University of Colorado Cancer Center in a statement.
The findings highlight the need for patients to be aware of the risk between infection and cancer spread.
For affected patients, "The simplest strategy would be to avoid infection (vaccination, avoiding crowded places during flu season, etc)," DeGregori told Newsweek.
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Breast cancer is the most common cancer in women. Around 316,950 new cases of invasive breast cancer will be diagnosed in women in the U.S. this year, with more than 42,000 women expected to die from the disease this year alone, according to the American Cancer Society.
After remission, cancer cells may remain dormant for years before spreading— notably in the lungs or other organs—and causing a relapse. As viral respiratory infections like SARS-CoV-2 (the virus that causes COVID-19) are associated with inflammation, this may trigger processes that could cause cancer cells to spread.
A rise in cancer death rates in the first two years of the pandemic led DeGregori and his colleagues to study the effects of the influenza virus and SARS-CoV-2 infections on breast cancer outcomes in mouse models. They determined that these infections reduced the dormancy of breast cancer cells in the lungs.
The cancer cells multiplied within days of infection, leading to the expansion of metastatic cancer lesions within two weeks. Inflammatory pathways are implicated in this effect, the researchers found.
"The study proves that the general phenomenon can also be observed in humans. Of course, the authors cannot prove that it is the same mechanism, as these are epidemiological data," said professor Carsten Watzl, Scientific Director of the Immunology Research Unit of the Leibniz Research Centre for Working Environment and Human Factors Dortmund.
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Analysis of molecules revealed that the awakening of dormant cancer cells is driven by a protein called interleukin-6 (IL-6), which immune cells release in response to infections or injuries.
"The identification of IL-6 as a key mediator in arousing DCCs from dormancy suggests that using IL-6 inhibitors or other targeted immunotherapies might prevent or lessen the resurgence of metastasis following viral infection," said paper author and MECCC cell biologist Julio Aguirre-Ghiso said in a statement.
The researchers also examined whether patients with cancer that tested positive for COVID-19 might have an increased risk of cancer-related death, analyzing data from the UK Biobank (4,837 participants, all cancer types) and Flatiron Health (36,845 patients with breast cancer) databases.
They discovered an association between SARS-CoV-2 infection and risk of death in the Biobank group. Patients that tested positive SARS-CoV-2 showed a twofold increase in cancer-related death compared to those who were negative.
In the Flatiron group, the infection was associated with an increase of more than 40 percent in the risk of metastatic disease in the lungs.
It should be noted the new study focused on the period before COVID-19 vaccines were available. Although the studies were limited to those previously diagnosed with cancer, or mice that had dormant cells already when infected, DeGregori cautioned that the team, "couldn't rule out an effect on those with active cancer."
Cell and molecular biologist John Alcorn of the University of Pittsburg told Newsweek, "This study does not address how bad of a COVID or flu infection is needed to trigger this type of response. Another prevention would be to have imaging done if you are a cancer patient in remission who gets a viral pneumonia. This could lead to early detection or resurgence and increased treatment options."
DeGregori added: "Additional research and clinical studies will be needed for the development of interventions that could be applied during the infection, and we are actively working to develop such interventions."
The researchers plan to extend their analyses, both in animal models and of clinical data, to other cancer types and areas of metastatic disease.
Do you have a tip on a health story that Newsweek should be covering? Do you have a question about breast cancer? Let us know via health@newsweek.com.
Reference
Chia, S. B., Johnson, B. J., Hu, J., Valença-Pereira, F., Chadeau-Hyam, M., Guntoro, F., Montgomery, H., Boorgula, M. P., Sreekanth, V., Goodspeed, A., Davenport, B., De Dominici, M., Zaberezhnyy, V., Schleicher, W. E., Gao, D., Cadar, A. N., Petriz-Otaño, L., Papanicolaou, M., Beheshti, A., Baylin, S. B., ... DeGregori, J. (2025). Respiratory viral infections awaken metastatic breast cancer cells in lungs. Nature. https://doi.org/10.1038/s41586-025-09332-0
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