Respiratory Infections May Reactivate Dormant Breast Cancer Cells, Study Finds
In a groundbreaking study published in Nature, researchers from the University of Colorado Anschutz Medical Campus, Montefiore Einstein Comprehensive Cancer Center (MECCC), and Utrecht University have uncovered the first direct evidence that common respiratory infections—such as COVID-19 and influenza—can awaken dormant breast cancer cells in the lungs, potentially leading to new metastatic tumors.
“Our findings indicate that individuals with a history of cancer may benefit from taking precautions against respiratory viruses, such as vaccination when available, and discussing any concerns with their healthcare providers,” said Julio Aguirre-Ghiso, Ph.D., co-leader of the study and director of the Cancer Dormancy Institute at MECCC.
Led by Dr. James DeGregori of CU Cancer Center, alongside Drs. Mercedes Rincon (CU Anschutz) and Roel Vermeulen (Utrecht University and Imperial College London), the study demonstrated how severe inflammation triggered by respiratory viruses can reawaken dormant disseminated cancer cells (DCCs)—cells that had previously migrated from the primary tumor and lay inactive in distant organs.
Viruses Ignite “Sleeper Cells”
Using specialized mouse models developed in Dr. Aguirre-Ghiso’s lab that mimic metastatic breast cancer dormancy in human lungs, researchers exposed mice to either SARS-CoV-2 or influenza viruses. In both cases, infections rapidly activated the dormant cancer cells, causing a surge in metastatic activity. Within two weeks, visible metastatic lesions formed.
“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 Dr. DeGregori.
The study identified interleukin-6 (IL-6), a protein released by immune cells during infection, as a key driver in reactivating dormant cancer cells. “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,” explained Dr. Aguirre-Ghiso.
Human Data Echo the Risk
In addition to the animal research, the team examined two large population studies to investigate whether COVID-19 infections were linked to increased cancer mortality or metastasis in survivors.
In the first, researchers used the UK Biobank, a cohort of over 500,000 individuals, to focus on cancer survivors who had been in remission for at least five years before the COVID-19 pandemic. Among 487 individuals who tested positive for COVID-19, compared to 4,350 matched controls who tested negative, there was nearly a twofold increase in cancer-related mortality—even after excluding those who died directly from COVID-19. “The effect was most pronounced in the first year after infection,” noted Dr. Vermeulen.
In a second study using the U.S.-based Flatiron Health database, researchers analyzed breast cancer patients from 280 clinics. Out of more than 36,000 patients, the 532 who contracted COVID-19 were nearly 50% more likely to develop lung metastases during a follow-up period of roughly 52 months.
“Our findings suggest that cancer survivors may be at increased risk of metastatic relapse after common respiratory viral infections,” said Dr. Vermeulen. He emphasized that these analyses occurred before COVID-19 vaccines became widely available.
Implications and Next Steps
The research highlights a previously underappreciated danger: that even long-dormant cancer cells may be reawakened by common illnesses. “Respiratory viral infections are forever a part of our lives, so we need to understand the longer-term consequences of these infections,” said Dr. DeGregori.
Looking forward, the team plans to explore whether similar mechanisms occur in other cancer types and metastatic sites. They also aim to identify targeted interventions—such as IL-6 blockers—that could protect vulnerable cancer survivors from viral-triggered relapse.
With respiratory viruses an ongoing global health concern, these findings underscore the importance of both infection prevention and further study into cancer dormancy and immune response.