Respiratory Infections Can Awaken Breast Cancer Metastases

Dormant breast cancer metastases can “reawaken” and progress suddenly. Inflammation at the sites where cancer cells metastasize is one well-known cause of cancer growth, and breast cancer often metastasizes to the lungs. So, are respiratory infections, which cause pulmonary inflammation, associated with breast cancer metastases?

An international team reports that, in mice, infection with either influenza virus or SARS-CoV-2 causes a >100-fold expansion of lung metastases within 2 weeks. The transition is dependent on the proinflammatory cytokine, interleukin-6 (IL-6), which activates the JAK-STAT signaling pathway. The disseminated cancer cells then “teach” CD4+ T cells to inhibit the CD8+ T cell response mounted against cancer cell proliferation.

Do these mouse studies have relevance to humans? When these researchers retrospectively studied nearly 37,000 women with known breast cancer, the chance of newly observed 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 who were infected by SARS-CoV-2 were 2.6 times more likely to die from cancer subsequently than those who were not infected, after multivariate adjustment. Risk was greatest shortly after infections and decreased over time.