Bacteria living inside cancerous tumors contribute to the formation of dangerous metastases for patients by increasing the resistance of defective cells during the progression of the disease, scientists of Westlake University (China) said.

During the study, which is reported in the journal Cell, experts experimented with a mouse model of breast cancer with a significant number of microorganisms in malignant cells.

It turned out that the bacteria can spread together with the defective cells through the bloodstream, contributing to tumor metastasis. The microorganisms can modulate the cellular actin network and promote cell survival under mechanical stress in the bloodstream. Just one injection of bacteria into a breast tumor can cause a tumor that initially had a low risk of metastasizing.

Although the study found a clear role for intratumor bacteria in promoting cancer cell metastasis, the authors do not rule out the possibility that the gut microbiome and immune system may act in concert with intratumor bacteria to determine cancer progression.

In the future, scientists plan to find out how bacteria penetrate tumor cells, how intracellular bacteria integrate into the host cell system, and how bacteria-containing tumor cells interact with the immune system.