The research highlights emerging scientific perspectives and underscores the importance of ongoing research and careful interpretation of such findings.
Published Aug 13, 2025 | 12:10 AM ⚊ Updated Aug 13, 2025 | 12:10 AM
Cancer. Representational Image. (Creative Commons)
Synopsis: A recent study has brought to light a possible connection between respiratory viruses like influenza and SARS-CoV-2 and the reactivation of dormant cancer cells in the lungs. Using laboratory models, the researchers demonstrated that viral infections can stimulate inactive breast cancer cells to begin proliferating, leading to the growth of metastatic tumours.
A recent study titled Respiratory viral infections awaken metastatic breast cancer cells in lungs has brought to light a possible connection between respiratory viruses like influenza and SARS-CoV-2 and the reactivation of dormant cancer cells in the lungs.
The research was led by Shi B Chia and Bryan J Johnson from the Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus in the United States.
Using laboratory models, the researchers demonstrated that viral infections can stimulate inactive breast cancer cells to begin proliferating, leading to the growth of metastatic tumours.
Importantly, this research also examined large human cancer databases and found an association between Covid-19 infection and increased cancer-related mortality, suggesting that respiratory viruses might play a role in cancer recurrence.
While these findings are significant and may offer new insights into how viral infections influence cancer progression, it is essential to approach the results with caution. This study is an early step in understanding a complex process, and further research is needed before drawing definitive conclusions.
This information highlights emerging scientific perspectives and underscores the importance of ongoing research and careful interpretation of such findings.
Breast cancer is the second most common cancer worldwide, with several deaths caused by metastasis, that is, cancer that spreads to other parts of the body, often after a long period, when cancer cells remain dormant, that is, in an inactive form.
Understanding what causes the dormant disseminated cancer cells (DCCs) — the cells that have spread but are not growing — to “wake up” and start growing again is critical to improving treatment and preventing cancer recurrence.
This study focused on whether respiratory viral infections such as influenza and SARS-CoV-2 might disrupt this dormancy and trigger the cancer to spread.
Using mouse models of breast cancer, the researchers studied how infections with influenza and SARS-CoV-2 viruses affected dormant cancer cells in the lungs. They found that these infections caused the dormant cells to lose their inactive state, leading to rapid growth within days and the formation of large metastatic tumours within two weeks.
These changes were driven by a specific immune signalling molecule called interleukin-6 (IL-6), which plays a role in inflammation. The study also showed that the immune system’s response to infection, particularly through a type of immune cell called CD4+ T cells, helped the cancer spread by reducing the activity of CD8+ T cells, which normally attack and kill cancer cells.
Importantly, these experimental findings in mice were supported by analyses of human cancer survivors using two large patient databases. The first was the UK Biobank, which included people diagnosed with various cancers before 2015 who had no known spread of cancer by the start of the Covid-19 pandemic.
The second was the Flatiron Health database, focusing on breast cancer patients in the United States. Both datasets showed that people infected with SARS-CoV-2 had a higher risk of cancer-related death and lung metastasis compared to those not infected.
Together, these results reveal a significant connection between respiratory viral infections and the reactivation of dormant metastatic breast cancer cells. The study highlights how infections like influenza and Covid-19 may influence cancer progression and points to the need for further research on how viral infections interact with cancer recurrence.
While the study’s findings from mouse models are compelling, speaking to South First, Dr Rajeev Jayadevan, a senior gastroenterologist and chairman of the Indian Medical Association (IMA) Research Cell, highlighted important limitations in relying on human patient databases to confirm these results.
“To explore whether a similar link might exist in humans exposed to respiratory viral infections such as SARS-CoV-2, the researchers analysed two large cancer patient databases,” he explained. However, he points out that these databases vary in many aspects, and their data must be interpreted carefully.
Dr Jayadevan elaborated that the first database, the UK Biobank, included individuals diagnosed with cancer before 2015 who had no known metastatic disease at the pandemic’s start. Comparing cancer outcomes between those who tested positive for Covid-19 in 2020 and those who did not, the study found that cancer-related mortality was nearly twice as high among infected individuals, especially within the first year after infection.
The second database, Flatiron Health, which focuses on breast cancer patients, showed a 40 percent increased risk of recurrence in those with prior Covid-19 infection. However, “The absolute risk, which applies to the individual, appears small,” he noted, giving the example that this might translate to about four additional cancer recurrences per 100 infected individuals over five years, if the link is genuine.
Dr Jayadevan urged caution when communicating such findings to the public: “It is essential to ensure that it does not induce unnecessary anxiety. The goal should be to convey information without creating fear. Unfortunately, many science articles use clickbait headlines that needlessly increase public anxiety.”
He stressed that scientific knowledge advances slowly and steadily, through multiple studies rather than a single one. “One study alone is not enough to redefine our understanding,” he said, adding that “publication bias” means studies with negative or inconclusive results often go unpublished, which can skew the apparent strength of evidence.
Describing the laboratory component, Dr Jayadevan summarised, “This study was conducted in two main parts. The first was a laboratory-based investigation using a mouse model of breast cancer. Researchers found that inactive cancer cells in the lungs became active and formed tumours after infection withthe influenza virus.”
He warned, while this animal model suggests that viral infections could awaken inactive cancer cells, “We are not certain whether this research applies to humans in the context of cancer.” He adds that “public anxiety is a side effect that must be taken seriously.”
He also commented on the immune response involved, explaining that during viral infections, the immune system produces inflammatory markers like interleukin-6 (IL-6), which may unintentionally stimulate dormant cancer cells to grow again. “Anyone with relatively compromised health, whether due to age, diabetes, heart disease, kidney failure, liver disease, or a history of cancer, should take care not to contract infections,” he said.
“Infection vulnerable people should avoid crowded birthday parties and refrain from visiting anyone with a viral fever, standard precautions of that sort,” he said, noting that difficulty in distinguishing deaths caused by cancer from those due to Covid-related lung complications when relying on medical records, as “the line between the two causes of death is often blurred.”
Dr Jayadevan emphasised that just because something is flagged in a study does not mean it is the absolute truth. If multiple studies point in the same direction, then we may recommend that people with cancer take special care to avoid viral infections. Until then, there is no such recommendation.
(Edited by Muhammed Fazil.)
