The role of liquid biopsy in management of the neck with indeterminate response on post-treatment imaging following non-surgical management of oropharyngeal cancer.

INTRODUCTION: This study aimed to determine if post-treatment HPV cell-free DNA (cfDNA) can assist in the decision-making process for salvage neck dissection in patients following non-surgical treatment of oropharyngeal squamous cell carcinoma (OPSCC) with a partial response in the neck on imaging at 12 weeks post-treatment. METHODS: 86 patients who completed treatment were prospectively recruited through the regional multidisciplinary team (MDT). Treatment response was categorised as complete response (CR), partial response (PR) or progressive disease on 12-week post-treatment imaging. Pre- and post-treatment blood samples were assessed for HPV cfDNA through droplet digital PCR (ddPCR). RESULTS: Eight patients had an isolated partial response in the neck. One (12.5%) had detectable HPV cfDNA (22.96 copies/ml) at ∼12 weeks post-treatment with positive disease on subsequent neck dissection (positive predictive value; PPV = 100%). Of the seven patients with undetectable HPV cfDNA, two patients had evidence of regional disease recurrence at 23.9 and 27.4 months respectively (negative predictive value; NPV = 71%). CONCLUSION: The detection of HPV cfDNA may help target salvage therapy in patients with a partial response in the neck. Follow-up studies in larger cohorts would be required to further validate the use of post-treatment HPV cfDNA in the management of OPSCC.

Longitudinal measurement of HPV copy number in cell-free DNA is associated with patient outcomes in HPV-positive oropharyngeal cancer.

INTRODUCTION: Oropharyngeal squamous cell carcinoma (OPSCC) is increasing in global prevalence and is divided into two types dependent on association with human papillomavirus (HPV). Assay of HPV copy number in plasma cell-free DNA (cfDNA) provides a minimally invasive method for detecting and monitoring tumour-derived HPV, with potential for enhancing clinical care. MATERIALS AND METHODS: In a prospectively recruited cohort of 104 OPSCC patients, we evaluate the utility of cfDNA droplet digital PCR (ddPCR) as a method for characterisation and longitudinal monitoring of patients with OPSCC. RESULTS: ddPCR assay of pre-treatment plasma cfDNA for five HPV types showed overall 95% concordance with p16 immunohistochemistry and PCR analysis of tumour tissue. Longitudinal sampling in 48 HPV+ve patients, with median follow-up of 20 months, was strongly associated with patient outcomes. Persistently elevated cfDNA-HPV post-treatment was associated with treatment failure (2/2 patients) and an increase of cfDNA-HPV in patients whose HPV levels were initially undetectable post-treatment was associated with disease recurrence (5/6 patients). No recurrence was observed in patients in whom cfDNA-HPV was undetectable in all post-treatment samples. In two patients, sequential HPV measurement could have avoided surgical intervention which did not confirm recurrence. CONCLUSION: The high concordance of pre-treatment plasma cfDNA-HPV analysis with tissue-based assays, together with the clinical associations of sequentially measured post-treatment cfDNA-HPV copy number add to a growing body of evidence that suggest utility of cfDNA-HPV ddPCR in management of OPSCC. Standardised clinical trials based on these data are now needed to assess the impact of such testing on overall patient outcomes.