New Delhi, July 31 Common respiratory infections, including Covid-19 and influenza, can awaken dormant breast cancer cells that have spread to the lungs, setting the stage for new metastatic tumours, according to a new study.
The findings published in the journal Nature, based on mouse studies as well as meta-analysis of human patients, support research showing increases in death and metastatic lung disease among cancer survivors infected with SARS-CoV-2 -- the virus that causes Covid.
"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 health care providers," said Julio Aguirre-Ghiso, from the Albert Einstein College of Medicine, US.
Previous evidence suggests that inflammatory processes can awaken disseminated cancer cells (DCCs) -- cells that have broken away from a primary tumour and spread to distant organs, often lying dormant for extended periods.
An increase in cancer death rates during the Covid pandemic bolstered the idea that severe inflammation may be waking up the dormant DCCs, Aguirre-Ghiso said.
The team tested the hypothesis on mice and exposed them to SARS-CoV-2 or the influenza virus -- both triggered the awakening of dormant DCCs in the lungs, leading to a massive expansion of metastatic cells within days of infection and the appearance of metastatic lesions within two weeks.
Molecular analyses revealed that the awakening of dormant DCCs is driven by interleukin-6 (IL-6), a protein that immune cells release in response to infections or injuries. This suggested that using IL-6 inhibitors or other targeted immunotherapies might prevent or lessen the resurgence of metastasis.
Further, to understand the implications in humans, the team analysed two large databases and found that respiratory infections in cancer patients in remission are linked to cancer metastasis.
"The effect was most pronounced in the first year after infection," said Roel Vermeulen, from Utrecht University, The Netherlands.
The rapid progression to cancer mirrors the observed quick expansion of dormant cancer cells in animal models.
"Our findings suggest that cancer survivors may be at increased risk of metastatic relapse after common respiratory viral infections," said Vermeulen. "It is important to note that our study focused on the period before Covid-19 vaccines were available."
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