A routine virus can slow breast cancer spread to the lungs, offering hidden protective power

Respiratory syncytial virus (RSV), mostly infects the lungs, nose, throat, and respiratory tract, and can cause illness ranging from mild cold and fever-like symptoms to severe pneumonia and bronchitis. A recent study has found that having a respiratory infection can act as a shield against the spread of cancer cells.

A natural antiviral chemical called type I interferons is produced by our body as one of the earliest responders in the fight against RSV infections. These molecules can also help prevent breast cancer from spreading to the lungs by changing the lung environment in a way that makes it difficult for cancer cells to survive or thrive. The findings are published in PNAS.

From infection to protection

The lungs may seem safely tucked inside the ribcage, but with every breath, they are in constant contact with the outside world. As we inhale air, lung cells are continuously exposed to germs, allergens, harmful gases, and pollution. While our immune system is designed to react strongly to anything foreign, the lungs must keep this response under control to avoid overreacting to everything we breathe in.

This carefully maintained calm can come at the cost of creating an environment where cancer cells can quietly settle and begin to grow. The spread of cancer cells can alter the biochemical environment of the lungs, and so can respiratory infections such as RSV or COVID. Not much is known about how respiratory infections and lung cancer metastasis interact. Do they support each other and coexist, or do they actually hold each other back?

In this study, the researchers explored this mystery with the help of a mouse model. They first exposed the mice to RSV, and then, exactly a day later, introduced breast cancer cells into their bloodstream.

They compared these mice with a control group that received the cancer cells but was not infected, allowing them to see whether the virus influenced the number of tumors formed in the lungs. They observed that in mice infected with RSV, cancer cells struggled to take hold and grow in the lungs, resulting in fewer metastatic tumors.

To ensure that immune cells weren’t interfering with this phenomenon, the team used specific antibodies to temporarily remove different types of immune cells one by one. Even after this, the anti-cancer effect of the lung infection remained almost entirely intact. This gave the researchers a hint that the help was coming from the lungs themselves.

When the body detects a virus, it sends out a chemical alarm signal called type I interferons—which include IFN- β and IFN- α subtypes, which are powerful antiviral proteins. To test the idea that these chemical signals might be preventing the cancer cells from invading, they treated healthy mice with lab-made interferons and waited for the molecules to block cancer—and they did.

Further investigation revealed that interferons don’t directly attack tumor cells. Instead, they reshape the lung’s own epithelial and endothelial cells, making it harder for cancer cells to enter the lung tissue from the bloodstream and find the support they need to grow into tumors.

The researchers also discovered that a protein called Galectin-9, activated by interferons, is elevated during this process and can directly prevent cancer cells from settling in the lungs.

These findings suggest that viral infections and type I interferons can reshape the lung environment in ways that hinder cancer from taking hold, which can be exploited when developing new anti-metastatic therapies. Before that can move forward, studies first need to show whether similar effects can be seen in humans.

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