Given the onset of a particular type of cancer, why does that cancer become a much worse prospect for only some individuals? Why are some people more prone to metastasis, for example? A perhaps underappreciated factor is the interaction of infectious agents with the tumor microenvironment, as researchers discuss here. Exposure to pathogens, and particularly persistent pathogens, may be a good explanation for many areas of medicine in which only some people bearing all of the traditional risk factors go on to develop the worst outcomes.
Microbes play a critical role in affecting cancer susceptibility and tumor progression, particularly in colorectal cancers. However, emerging evidence suggests that they are also integral components of the tumor tissue itself in in a broad range of cancer types, such as pancreatic cancer, lung cancer, and breast cancer. Microbial features are linked to cancer risk, prognosis, and treatment responses, yet the biological functions of tumor-resident microbes in tumor progression remain unclear.
Whether these microbes are passengers or drivers of tumor progression has been an intriguing question. Researchers used a mouse model of breast cancer with significant amounts of bacteria inside cells, similar to human breast cancer. They found that the microbes can travel through the circulatory system with the cancer cells and play critical roles in tumor metastasis. Specifically, these passenger bacteria are able to modulate the cellular actin network and promoted cell survival against mechanical stress in circulation.
"We were surprised initially at the fact that such a low abundance of bacteria could exert such a crucial role in cancer metastasis. What is even more astonishing is that only one shot of bacteria injection into the breast tumor can cause a tumor that originally rarely metastasizes to start to metastasize. Intracellular microbiota could be a potential target for preventing metastasis in broad cancer types at an early stage, which is much better than to have to treat it later on."