A recent study by an international research team has found that common respiratory infections, such as influenza or COVID-19, could awaken dormant cancer cells in the body, leading to lung metastasis in breast cancer patients years after their initial recovery. This discovery has attracted significant attention from the global medical community.
Cancer Cells May Not Disappear Completely — They Lie Dormant, Waiting for a Trigger
Breast cancer is the second most common cancer worldwide. Many patients, even after undergoing surgery, radiotherapy, or chemotherapy, may still harbor a small number of cancer cells in their body. These cells, known as Dormant Cancer Cells (DCCs), are in a state of inactivity.
Unlike active cancer cells that multiply rapidly and spread, dormant cancer cells can sleep in the body for years without causing any symptoms or being detected by routine medical tests. However, this new study suggests that certain viral infections, especially those affecting the respiratory system (such as influenza or COVID-19), could disrupt this delicate balance.
Influenza and COVID-19 Can Reactivate Dormant Cancer Cells
In mouse experiments, scientists observed that after infection with the influenza virus or SARS-CoV-2 (the virus responsible for COVID-19), dormant breast cancer cells in the lungs began to multiply within just a few days. Within two weeks, visible tumors had formed in the lungs.
The underlying mechanism of this phenomenon involves a protein called Interleukin-6 (IL-6), which is produced by the immune system in response to infection. IL-6 serves as a crucial signal molecule that mobilizes the body’s defense mechanisms. However, the study revealed that an excessive release of IL-6 can inadvertently wake up dormant cancer cells, becoming a driver of cancer recurrence and metastasis.
The Immune System Gets Distracted, Giving Cancer Cells an Opportunity
Beyond directly activating cancer cells, these viral infections also interfere with the body’s ability to fight cancer. Specifically, T cells—immune cells responsible for identifying and eliminating cancer cells—become less effective when the immune system is preoccupied with fighting a viral infection. The study highlighted that CD8+ T cells, which act as the immune system’s killer cells, were suppressed by CD4+ T cells during infection, giving cancer cells a chance to grow unchecked.
In simple terms, while the body is busy battling the virus, it becomes less vigilant against cancer cells lying in wait.
Human Data Confirms: Higher Recurrence Risk for Cancer Survivors After COVID-19 Infection
To validate whether this mechanism also occurs in humans, the research team analyzed two large real-world databases:
UK Biobank: A long-term health tracking database covering hundreds of thousands of cancer survivors.
Flatiron Health Database: Focused on treatment and follow-up data for breast cancer patients.
The findings were concerning: breast cancer survivors who had contracted COVID-19 showed a significantly higher risk of cancer recurrence and lung metastasis compared to those who had not been infected. This data reinforces the long-term and far-reaching impact of respiratory infections on cancer relapse.
Virus Infections Are Far More Than Just The Flu
As influenza and COVID-19 become permanent fixtures in our environment, this study serves as a critical reminder: the health impacts of viral infections go far beyond a simple cold. For cancer survivors, preventing infections and closely monitoring infection history will become essential components in managing the risk of cancer recurrence.
