New Study Finds a Significant Link Between Respiratory Illness and Breast Cancer

A joint study by researchers at three institutions, finds that breast cancer survivors, regardless of how long they’ve been in remission, need to be very careful about contracting respiratory illness. 

In the July 2025 issue of Nature, researchers reported that common respiratory illnesses, including the flu or Covid, can awaken dormant breast cancer cells.

After noticing an odd uptick in cancer cases since the COVID-19 pandemic, medical researchers at the University of Colorado Anschutz Medical Campus, Montefiore Einstein Comprehensive Cancer Center (MECCC), and Utrecht University in the Netherlands began investigating the correlations between these respiratory illnesses and this increase in cancer cases.

For years, scientists have hypothesized that certain viruses have the potential to trigger certain cancers. Some diseases are also confirmed to trigger cancer, such as human papillomavirus (HPV).

Scientists have been looking since 1936 for viruses that increase breast cancer, although that research mostly studied mice. The newest findings illustrated instances of high-risk viruses in human breast cancer samples.

The Epstein-Barr Virus, a common and highly contagious infection that causes fever and fatigue, can lead to someone having a five times higher ratio of breast cancer tissue than those without the disease. Researchers say this connection, however, is still just a hypothesis.

In this new study, researchers gave mice dormant cancer cells in their lungs and then exposed them to SARS-CoV-2 or influenza virus. In both cases, respiratory viruses awoke dormant cells, leading to an immense expansion of metastatic cells within only days of infection. Metastatic lesions could be seen within two weeks of infection. 

James DeGregori, Ph.D., deputy director of the Colorado University Cancer Center, served as supervising author on the study, and said that "dormant cancer cells are like the embers left in an abandoned campfire, and respiratory viruses are like a strong wind that reignites the flames".

Julio Aguirre-Ghiso, Ph.D., one of the study’s co-leaders, director of MECCC’s Cancer Dormancy Institute and the Rose C. Falkenstein Chair in Cancer Research at Albert Einstein College of Medicine, made the connection clear, stating, "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 healthcare providers".

The findings in mice were supported by additional patient research dating to the beginning of the pandemic, showing an uptick in metastatic lung disease and death in cancer survivors with SARS-CoV-2 infections.

University of Colorado Anschutz School of Medicine researchers examined female breast cancer patients in U.S. cancer clinics. In the 52-month follow up period, it determined that those who had contracted Covid were more than 50% more likely to have metastatic progression in their lungs versus patients who did not.

Researchers at Utrecht University in the Netherlands focused on patients who had been diagnosed with cancer but were likely in remission. Their work found that patients' risk of dying from cancer doubled if they had COVID-19, versus cancer patients who did not (excluding those who succumbed to the virus). This doubling effect was most prominent in the first year after remission.

 Both human and animal research in the Colorado, Utrecht and MECCC studies shows a significant expansion of metastatic cells within days of infection and metastatic lesions within two weeks.

"The extent of this increased risk is almost unheard of in epidemiology for cancer," said Utrecht University epidemiologist Roel Vermeulen, Ph.D.

The key takeaway: the immune system fights viruses in a way that creates the perfect conditions for cancer to grow.

For women, the most commonly diagnosed cancer is breast cancer. For many, remission is not the end of the illness, cancer cells can remain dormant for years before relapse is induced by metastasis. It is important to protect yourself and stay hypervigilant, to try and prevent relapse when possible.