Monotonic dysregulation of genes and pathways during progression from normal through leukoplakia to gingivo-buccal oral cancer identified, and a significant role of interferons in activating tumor immune evasion detected

Oral squamous cell carcinoma of the gingivo-buccal region (OSCC-GB) accounts for the highest cancer morbidity and mortality among men in India. It has been observed that about one-third of individuals with oral leukoplakia, a dysplastic precancerous lesion in the oral cavity, progress to oral cancer. We aimed to identify systematic transcriptomic changes as a normal tissue in the oral cavity progresses to frank OSCC-GB. Seventy-two OSCC-GB patients, from multiple hospitals, were recruited and transcriptome analysis of tumor and adjacent normal tissue (of all patients), and adjacent leukoplakia tissue (of a subset of 25 unselected patients with concomitant leukoplakia) was performed. We have identified many differences in the transcriptomic profiles between OSCC-GB and squamous cell carcinoma of the head and neck regions. Compared to precancerous tissues, significant enrichment of ECM-receptor interaction, PI3K-Akt signaling, cytokine-cytokine receptor interaction, focal adhesion, cell cycle pathways were observed in OSCC-GB. Using gene set enrichment analysis, we identified a profound role of interferon receptor signalling in tumor growth by activating immune evasion mechanisms. The role of tumor-infiltrating immune cells further supported the growth and immunosuppressive mechanism of tumor tissues. Some immune evasion genes - CD274, CD80, and IDO1 - were found to be activated even in the precancerous tissue. Taken together, our findings provide a clear insight into the sequential genetic dysregulation associated with progression to oral cancer. This insight provides a window to development of predictive biomarkers and therapeutic targets for gingivo-buccal oral cancer.