The genomic architectures of tumour-adjacent tissues, plasma and saliva reveal evolutionary underpinnings of relapse in head and neck squamous cell carcinoma

Background Head and neck squamous cell carcinoma (HNSCC) is characterised by a dismal prognosis; nonetheless, limited studies have unveiled the mechanisms underlying HNSCC relapse. Methods Next-generation sequencing was performed to identify the somatic mutations in 188 matched samples, including primary tumours, tumour-adjacent tissues (TATs), pre- and post-operative plasma, saliva and peripheral blood lymphocytes (PBLs) from 27 patients. The evolutionary relationship between TATs and tumours were analysed. The dynamic changes of tumour- and TAT-specific mutations in liquid biopsies were monitored together with survival analysis. Results Alterations were detected in 27 out of 27 and 19 out of 26 tumours and TATs, respectively. TP53 was the most prevalently mutated gene in TATs. Some TATs shared mutations with primary tumours, while some other TATs were evolutionarily unrelated to tumours. Notably, TP53 mutations in TATs are stringently associated with premalignant transformation and are indicative of worse survival (hazard ratio = 14.01). TAT-specific mutations were also detected in pre- and/or post-operative liquid biopsies and were indicative of disease relapse. Conclusions TATs might undergo the processes of premalignant transformation, tumorigenesis and eventually relapse by either inheriting tumorigenic mutations from ancestral clones where the tumour originated or gaining private mutations independent of primary tumours. Detection of tumour- and/or TAT-specific genetic alterations in post-operative biopsies shows profound potential in prognostic use.