Comprehensive Sequencing Study Finds Limited Connection Between Microbiome and Cancer

Recent extensive research by scientists at Johns Hopkins Medicine has challenged previous claims linking microbial communities to various human cancers. Over the past five years, multiple studies suggested that bacteria, viruses, and fungi residing in or on the body could be associated with different cancer types, creating optimism about microbiome-based diagnostics. However, the latest study, which sequenced human cancer tissues and analyzed microbial DNA content, found significantly fewer microbial sequences than earlier reports. The team analyzed 5,734 tissue samples from 25 cancer types, stored in The Cancer Genome Atlas (TCGA). They meticulously removed human DNA and potential contaminants—DNA from sequencing environments or handling—and compared the remaining sequences against an extensive database of microbial genomes. After this rigorous filtering, the average microbial DNA in solid tumors was just over half a percent, with some blood cancers showing slightly higher levels. Compared to prior studies, especially a now-retracted paper published in Nature five years ago, the current research detected far fewer microbial reads, suggesting earlier findings may have been influenced by contamination. The team identified familiar microbes associated with cancer, such as HPV and Helicobacter pylori, but also found common laboratory contaminants like baker's yeast and plant viruses, which are unlikely to impact human health. Importantly, the findings underscore the importance of careful contamination control and validation in microbiome research, especially as efforts to harness microbiome data for early cancer diagnosis intensify. The full sequencing data is now publicly accessible for further scientific investigation. This research emphasizes that, contrary to some previous beliefs, microbes play a minimal role within cancer tissues, urging caution in interpreting microbiome associations in cancer studies.