Respiratory viruses trigger metastatic breast cancer cells to proliferate in lungs in mouse models of breast cancer, a study in Nature indicates. These findings are supported by human observational data. The work sheds light on the association between infectious diseases and cancer metastasis. 

 Breast cancer is the most diagnosed cancer in women. After an initial remission, cancer cells may remain dormant for years before metastasis (in the lungs or other organs) causes a relapse. Viral respiratory infections, such as SARS-CoV-2, are associated with inflammation, which may trigger processes that could influence metastasis. 

An increase in cancer death rates in the first two years of the COVID-19 pandemic prompted James DeGregori and colleagues to study the effects of influenza virus and SARS-CoV-2 infections on breast cancer outcomes in mouse models. They found that these infections reduced the dormancy of breast cancer cells in the lungs. These cells proliferated within days of infection and led to the expansion of metastatic cancer lesions within two weeks. The authors find that inflammatory pathways are implicated in this effect. 

The authors also examined whether patients with cancer that tested positive for SARS-CoV-2 might have an increased risk of cancer-related death. They analysed data from the UK Biobank (4,837 participants, all cancer types) and Flatiron Health (36,845 patients with breast cancer) databases. There was an association between SARS-CoV-2 infection and risk of death in the Biobank group; patients that tested positive versus negative for SARS-CoV-2 showed a twofold increase in cancer-related death. In the Flatiron group, SARS-CoV-2 infection was associated with an increase of over 40% in the risk of metastatic disease in the lungs. 

Together, the findings reveal how respiratory virus infections may increase the risk of cancer relapse and highlight the need for strategies to address the increased risk of metastatic progression associated with respiratory virus infections, the authors conclude. 

Source: Nature