There is new compelling evidence that COVID-19 and other respiratory infections can reactivate dormant cancer cells. This can trigger the growth of secondary lung cancers. Inflammation at sites where cancer cells metastasize is one well known cause of cancer growth and breast cancer often metastasizes to the lungs. Most women who die of breast cancer do so when the cancer goes from remission or dormancy to actively dividing and growing again. These active cancer cells then spread to other parts of the body. Finding out why and how dormant cancers start to spread is key to improving cancer survival rates. Are respiratory infections and reactivation of breast cancer metastases real?
After initial remission, disseminated cancer cells (DCCs) can stay dormant for years to decades before metastatic relapse, which most commonly presents in lung, bone and liver. As these cancer cells duplicate some of them will circulate around the body in the bloodstream and lodge in other parts of the body. Secondary cancers will develop in those areas. This is known as metastatic progression- one cancer becoming several cancers. Unfortunately, increased inflammation, such as influenza or COVID-19 can be sufficient to increase metastasis. A study in mice found that infection with either influenza virus or SARS-CoV-2 (COVID-19) causes a >100 fold expansion of lung metastases within 2 weeks. The transition is dependent on a pro-inflammatory cytokine, interleukin-6 (IL-6) which activates the signaling of other pathways which inhibits certain T-cells response against cancer cell proliferation.
Among nearly 5000 people with cancer of any type in remission, those infected with SARS-CoV-2 were 2.6 times more likely to die from cancer subsequently than those who were not infected.
You might ask if those mouse studies have any relevance to humans. Well, when these researchers retrospectively studied nearly 37,000 women with known breast cancer, the chance of new pulmonary metastases was 1.4 times higher in those who received COVID-19 diagnoses than in those who didn’t. Among nearly 5000 people with cancer of any type in remission, those infected with SARS-CoV-2 were 2.6 times more likely to die from cancer subsequently than those who were not infected. The risk was greatest shortly after infections and then diminished over time.
So what does this mean and what can we do? This study indicates cancer survivors who contracted COVID or Influenza had a statistically higher risk of cancer-related deaths compared to uninfected cancer survivors. Those with cancer should do everything possible to lower exposure of respiratory infections and to be immunized against them- at least for influenza and SARS CoV-2, and possibly other viral (RSV) and bacterial (Pneumococcal vaccine) pulmonary pathogens.
References: Chia SB et al. Respiratory viral infections awaken metastatic breast cancer cells in lungs. Nature 2025 Jul 30; [e-pub]. (https://doi.org/10.1038/s41586-025-09332-0)
Anderer S. COVID-19, Flu May Reawaken Dormant Cancer Cells. JAMA. 2025;334 (12): 1047-1048. (https://doi.org/10.1001/jama.2025.14772)