Malassezia May Contribute to Basal Cell Carcinoma Development via Inflammatory and Oxidative Stress Pathways.

Basal cell carcinoma (BCC) is the most common malignant skin tumor. Skin-resident lipophilic Malassezia yeasts are associated with various cutaneous disorders, while their correlative patterns and potential biological effects in BCC tissues remain insufficiently defined. We used RT-qPCR screening of archived FFPE BCC specimens and metagenomic sequencing of three paired fresh tumor and peritumoral tissues to characterize tissue-associated Malassezia colonization. M. globosa was the most abundant species in FFPE samples and was also detectable in fresh tissues. In vitro functional assays (CCK-8, EdU) in HaCaT keratinocytes and A-431 epidermoid carcinoma cells showed that 12 h stimulation with optimal concentrations of M. globosa (1.2 × 107 CFU/mL) and M. yamatoensis (1.6 × 107 CFU/mL) significantly promoted epithelial cell proliferation. Transcriptome sequencing and subsequent RT-qPCR validation further showed that both strains significantly upregulate pro-inflammatory genes (IL-1β, IL-6, TNF-α) and oxidative stress-related genes (SOD1, SOD2) in these cell lines. Collectively, our findings describe a correlative association between Malassezia colonization and BCC lesions and offer preliminary in vitro mechanistic clues.