Viral Infections Reawaken Dormant Cancer Cells, Increasing Relapse Risk

According to recent research, common respiratory infections such as the flu or COVID-19 pose a serious threat to cancer survivors, as they can reawaken dormant cancer cells and increase the risk of metastasis and relapse.

The study, conducted on mice with engineered breast cancer cells, found that within days of being infected with the influenza or SARS-CoV-2 virus, the once-dormant cancer cells began to rapidly multiply and form new metastatic lesions in the lungs. Surprisingly, this process was not driven by the viruses themselves, but rather by the body's immune response to the infection.

The key culprit appears to be a secreted molecule called interleukin-6 (IL-6), which surges during viral infections and creates the perfect conditions for dormant cancer cells to shift from a dormant state to a highly active, dividing state. When the researchers disabled IL-6 in the mice, the dormant cancer cells did not multiply as much when the viral infection was introduced.

The danger doesn't end there. After each infection, there were dramatically more awakened cancer cells in the lungs, primed to begin multiplying again once triggered. This creates a greater risk for future relapses, as each episode magnifies the threat.

The researchers also found that the body's immune system, instead of destroying the reawakened cancer cells, actually shields them from further attacks, allowing the cancer to cleverly hijack the body's defenses.

While these findings were observed in mice, the researchers also analyzed data from thousands of cancer survivors in the UK and US during the COVID-19 pandemic. They found that cancer patients, especially those who had recently had respiratory infections, faced nearly double the risk of dying from cancer compared to those who did not get infected.