Strong evidence suggests that the human microbiome has an impact on tumourigenesis, the progression of cancer and the responses to cancer therapy. In contrast to cancer-associated bacteria, little is known about the role of fungi in human cancer and conclusive links remain elusive. Now, two new studies report comprehensive analyses of the fungal communities associated with cancer (that is, the cancer mycobiome). In the first study, Narunsky-Haziza et al. characterized the mycobiome of tissue, blood and plasma samples of patients across 35 cancer types from independent cohorts. The authors report the presence of fungal communities with different compositions across the various cancer types, indicating cancer type-specific fungal signatures. Histological staining showed that intra-tumour fungi exhibited cancer type-specific localization patterns as well as spatial association with macrophages and cancer cells. Finally, bacterial abundance and diversities were higher than those of the fungal communities, and both communities coexisted in the same niche, suggesting that the tumour microenvironment is a non-competitive space for microbial colonization. In the second study, Dohlman et al. analysed cohort samples from multiple body sites and reported that the samples harboured tumour-associated mycobiomes, and the authors went on to determine the fungal composition of these samples. Fungal DNA was abundant in lung tissues and specific sites in the gastrointestinal tract, and was particularly abundant in head-neck tissues, colorectal tissues and stomach tissues. Moreover, the authors found that live Candida species were enriched in tumour samples and that tumour-associated Candida species’ DNA was predictive of decreased survival. In stomach cancer, Candida species were associated with an increased expression of pro-inflammatory immune pathways, whereas in the lower gastrointestinal tract, Candida was associated with metastasis and deregulation of genes involved in maintaining cellular focal adhesions. On the basis of the findings, fungal DNA may serve as potential prognostic and diagnostic markers.