Setting higher standards for reports of microbial species in human cancers.

The presence of microbiota in human tumors has been reported widely based on bioinformatic analyses of DNA sequencing datasets; however, the source of microbial sequences in atypical anatomical sites is challenging to validate, as these could derive from sampling, storage, handling and processing of samples, similar to what has been described in studies of ancient DNA. Contamination of microbial reference genomes can also be a source of microbial signals, causing misclassification of human reads. Here, we overview the required quality controls and validation approaches and summarize optimal practices to improve the rigor and standards of tumor microbiome studies.