Different human tumour types each harbour their own unique bacterial communities, researchers report in a new study that profiled the microbiomes of more than 1,500 individual tumours across seven types of human cancer - the most comprehensive tumour microbiome study to date.
It has long been known that bacteria are present in tumours that originate from tissues routinely exposed to microbes (e.g., the gastrointestinal tract) but whether they are present in tumours arising from "sterile" tissues has been less clear.
Deborah Nejman and colleagues collected over 1,500 tumour samples and samples of adjacent normal tissue from nine medical centres in four countries.
The samples included melanoma, bone and brain cancer, tumour types whose association with bacteria had not previously been explored.
Applying a variety of methods to detect bacterial DNA, RNA and protein, and taking rigorous measures to exclude contamination, they found that most tumours and their adjacent normal tissues harbour bacteria.
Different tumour types had distinct microbiomes, with breast tumours displaying a particularly rich and diverse community of bacteria.
What's more, the authors found that bacteria within the tumours were present in both cancer cells and immune cells.
While there were intriguing associations between specific species of intra-tumour bacteria and factors such as patient smoking status, further work will be required to determine whether and how intratumour bacteria contribute to tumour development, progression, and response to therapy.
"Achieving a comprehensive understanding of the tumour microenvironment is a daunting yet critical step toward an organism-wide mechanistic model of cancer progression and, if successful, may unlock the next wave of precision cancer diagnostics and therapeutics," write Chloe Atreya and Peter Turnbaugh in a related Perspective.