Mycobiome and Cancer: What Is the Evidence?

SIMPLE SUMMARY: Although comprising a much smaller proportion of the human microbiome, the fungal community has gained much more attention lately due to its multiple and yet undiscovered interactions with the human bacteriome and the host. Head and neck cancer carcinoma, colorectal carcinoma, and pancreatic ductal adenocarcinoma have been associated with dissimilarities in the composition of the mycobiome between cases with cancer and non-cancer subjects. In particular, an abundance of Malassezia has been associated with the onset and progression of colorectal carcinoma and pancreatic adenocarcinoma, while the genera Schizophyllum, a member of the oral mycobiome, is suggested to exhibit anti-cancer potential. The use of multi-omics will further assist in establishing whether alterations in the human mycobiome are causal or a consequence of specific types of cancers. ABSTRACT: Background: To date, most researchhas focused on the bacterial composition of the human microbiota. In this review, we synopsize recent data on the human mycobiome and cancer, highlighting specific cancer types based on current available evidence, presenting interesting perspectives and limitations of studies and laboratory methodologies. Recent findings: Head and neck cancer carcinoma (HNCC), colorectal carcinoma (CRC) and pancreatic ductal adenocarcinoma (PDA) have been associated with dissimilarities in the composition of mycobiota between cancer cases and non-cancer participants. Overall, fungal dysbiosis with decreased fungal richness and diversity was common in cancer patients; however, a specific mycobiotic signature in HNSCC or CRC has not emerged. Different strains of Candida albicans have been identified among cases with HNCC, whilst Lichtheimia corymbifera, a member of the Mucoraceae family, has been shown to predominate among patients with oral tongue cancer. Virulence factors of Candida spp. include the formation of biofilm and filamentation, and the secretion of toxins and metabolites. CRC patients present a dysregulated ratio of Basidiomycota/Ascomycota. Abundance of Malassezia has been linked to the occurrence and progression of CRC and PDA, particularly in animal models of PDA. Interestingly, Schizophyllum, a component of the oral mycobiome, may exhibit anti-cancer potential. Conclusion: The human mycobiome, per se, along with its interactions with the human bacteriome and the host, may be implicated in the promotion and progression of carcinogenesis. Fungi may be used as diagnostic and prognostic/predictive tools or treatment targets for cancer in the coming years. More large-scale, prospective, multicentric and longitudinal studies with an integrative multi-omics methodology are required to examine the precise contribution of the mycobiome in the etiopathogenesis of cancer, and to delineate whether changes that occur in the mycobiome are causal or consequent of cancer.