DENVER, Aug. 4, 2025 – Viral infections like influenza and COVID-19 can dramatically increase the spread of breast cancer in mice, potentially by reactivating dormant cancer cells and hindering the immune system’s ability to fight them, according to a new study.
Viral infections may turbocharge breast cancer metastasis
New research suggests viruses can awaken dormant cancer cells and create a more aggressive cancer environment.
- Viral infections like influenza and COVID-19 significantly increased metastatic breast cancer in mice.
- Dormant cancer cells became active and morphed into a hybrid state after infection.
- Inflammatory protein IL-6 appears to play a role in reactivating these dormant cells.
- Immune cells meant to fight cancer may inadvertently protect it following viral exposure.
Researchers at the University of Colorado School of Medicine developed a specialized mouse model designed to mimic metastatic breast cancer in humans, including dormant cancer cells that have spread to other organs. These mice were engineered to overexpress a gene similar to HER2, a protein known to fuel rapid breast cancer cell growth.
James DeGregori, a biochemistry professor and senior author of the study, explained that this model simulates the long-term progression of breast cancer in patients, spanning years or even decades. The team exposed these mice to either influenza viruses or SARS-CoV-2, the virus that causes COVID-19.
The results were striking: the metastatic cancer burden in the mice jumped between 100-fold and 1000-fold. This surge occurred because the viral infections prompted dormant cancer cells to evolve into a previously unobserved hybrid state, indicating the infection itself stimulated cancer cell activation.
What’s the key factor driving this aggressive cancer spread?
Molecular analysis revealed that interleukin-6 (IL-6), an inflammatory protein released by immune cells during infection or injury, was responsible for reactivating the dormant cancer cells.
Previous research has also linked inflammation, and IL-6 specifically, to the development of metastatic tumors. Beyond IL-6, the study found that CD4 cells, a type of immune T cell, appeared to suppress anti-tumor activity after viral infection. This immune response change made it significantly harder to eliminate the cancer cells.
“Instead of the immune system actively eliminating the cancer cells, it protects them from immune elimination,” DeGregori stated. “We need to better understand this mechanism of immune suppression so that perhaps we can reverse it and allow the immune system to better control the cancer.”
