Droplet digital PCR quantification suggests that higher viral load correlates with improved survival in HPV-positive oropharyngeal tumours

Stevenson, A. and Wakeham, K. and Pan, J. and Kavanagh, K. and Millan, D. and Bell, S. and McLellan, D. and Graham, S.V. and Cuschieri, K. (2020) Droplet digital PCR quantification suggests that higher viral load correlates with improved survival in HPV-positive oropharyngeal tumours. Journal of Clinical Virology, 129. 104505. ISSN 1386-6532 (https://doi.org/10.1016/j.jcv.2020.104505)

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Abstract

Background.  Although HPV-positive oropharyngeal cancer (OPC) patients have improved prognosis compared to HPV negative patients; there remains an HPV-positive group who have poor outcomes. Biomarkers to stratify discrete patient outcomes are thus desirable. Our objective was to analyse viral load (VL) by droplet digital PCR (ddPCR), in HPV-positive patients with OPC on whom clinical outcome data were available. Methods.  In a cohort of patients that had previously tested HPV positive via conventional PCR, VL was determined using ddPCR assays for HPV16 L1 and E6 genes. VL was classed as “medium/high” if more than 5.57 copies or 8.68 copies of the HPV 16 L1 or E6 gene were detected respectively. Effect of VL on overall survival and hazard of death & disease progression was performed with adjustments made for sex, age, deprivation, smoking, alcohol consumption and stage. Results.  L1 VL ranged from 0.0014 to 304 gene copies per cell with a mean of 30.9; comparatively E6 VL ranged from 0.0012 to 356 copies per cell with a mean of 37.9. Univariate analysis showed those with a medium/high VL had a lower hazard of death; this was significant for L1 (p=0.02) but not for E6 (p=0.67). The ratio of E6 to L1 deviated from n=1 in most samples but had no influence on clinical outcomes. Conclusions.  HPV viral load may be informative for the further stratification of clinical outcomes in HPV positive OPC patients

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