Associate Professor Lagos State University College of Medicne Ikeja, Lagos, Nigeria
Abstract: Statement of the Problem Proliferative verrucous leukoplakia (PVL) is a rare type of white oral lesion first described in 1985 by Hansen et al (1). It typically begins as a single or multiple white patches in the mouth, and in 40-80% of cases, gradually progress to invasive oral squamous cell carcinoma (OSCC). Additional clinical characteristics include a high tendency for recurrence after excision of first episode of oral leukoplakia, and in most cases, the notable absence of known environmental carcinogens. The typical confluent exophytic (warty) proliferative appearance observed in PVL suggests a viral aetiology i.e., human vapilloma Virus (HPV). Prevention and diagnostic accuracy remains a challenge and prognosis is mostly poor due to resistance to standard therapeutic measures.
Materials and methods used in the investigation of the problem DNA from five PVL-OSCC and paired blood samples were subjected to whole exome sequencing and somatic mutations common in the tumours identified and validated across a larger PVL and conventional OSCC (Non PVL induced OSCC) cohort, used for control. DNA from three PVL-OSCC (two of which are same samples of the five PVL_OSCC cohort), were subjected to whole genome sequence and genome data filtered through the human reference genome and the resulting non-human fractions aligned to the viral reference sequence to generate paired matching data.
Method of data analysis Validation of selected PVL-OSCC somatic mutations was undertaken by pyrosequencing. Basic local alignment search tool (BLAST) National center for biotechnology information (NCBI) results of the non-human files from the 3 WGS samples was used to produce a summary table of top 5 viral paired hits.
Results of investigations PIK3CA E545K mutation frequency in the PVL-OSCC expanded cohort was 20% with none recorded in the conventional OSCC cohort, which recorded 28% of E542K mutation. Notably, 2 of the 3 early stage PVL samples demonstrating PIK3CA E545K mutations, was also corroborated in its advanced or PVL - OSCC equivalent. The pox virus, BeAn 58058 had the most BLAST hit recorded and all 212 hits from all three samples were from a specific 332bp subscript found between amino acid positions 8298bp – 8629bp of the BeAn viral genome.
Outcome data There remains a shortage of comprehensive data on PVL-OSCC transformation (2). This study suggested a distinct PIK3CA mutation type and pattern between PVL-OSCC and cOSCC and two third of the PVL-OSCC displaying E545K mutation were observed in the early low grade PVL equivalent suggesting this to be a possible early event. Should this be validated, it would provide a path to prediction or early detection which is advocated to prevent disease progression to oral cancer. The detection of a pox virus subscript following filtering with non-human sequence could have been due to an isolated presence or remnant following genetic integration.
Conclusions relevant to the problem This study suggested a mutation distinction between PVL - OSCC and the conventional OSCC with evidence supportive of it being an early-stage event. A digital transcriptome subtraction to look for fusion transcripts or to determine if the viral genome is transcriptionally active, as described in the Merkel cell carcinoma study is being suggested as a future study.
List two references 1. HANSEN, L. S., OLSON, J. A. & SILVERMAN, S., JR. 1985. Proliferative verrucous leukoplakia. A long-term study of thirty patients. Oral Surg Oral Med Oral Pathol, 60, 285-98. 2. OKOTURO, E. M., RISK, J. M., SCHACHE, A. G., SHAW, R. J. & BOYD, M. T. 2018. Molecular pathogenesis of proliferative verrucous leukoplakia: a systematic review. Br J Oral Maxillofac Surg, 56, 780-785.