Liquid Biopsy in Head and Neck Cancer

Background

Head and neck squamous cell carcinoma (HNSCC) stands as the sixth most common cancer worldwide. The overall 5-year survival is approximately 50 % due to often advanced clinical stage at diagnosis, high rate of treatment resistance, and high incidence of second cancers. Currently there are no useful biomarkers for surveillance or diagnosis of recurrent HNSCC.

Liquid biopsy (LB)

Circulating tumor DNA (ctDNA) is tumor-derived fragmented DNA circulating freely in the bloodstream. Apoptosis and necrosis due to rapid cell growth and increased cell turnover contribute to release of ctDNA in circulation of patients with cancer even without disseminated disease. ctDNA reflects tumor genome and may also reflect disease burden. Due to these properties and easy accessibility collection of ctDNA through venous blood has been termed as 'liquid biopsy'. Approximately 75-90 % of patients with localized or untreated HNSCC are expected to show ctDNA pre-treatment.

Applications of liquid biopsy in HNSCC

Potential clinical applications of liquid biopsy (LB) are manifold and include diagnosis of recurrence or progression, and disease surveillance. While ctDNA contains the same mutations present in original tumor, LB can be used to guide targeted therapies if local treatment is not feasible. In HNSCC, these features render study of LB attractive since early diagnosis of treatment failure increases possibilities for curative approach. ctDNA reflects tumor heterogeneity and findings in surveillance samples are more likely to characterize resistant subpopulations compared to pre-treatment changes. Recently, immune checkpoint inhibition with monoclonal antibodies against programmed cell death (PD-1) have demonstrated activity against recurrent or metastatic HNSCC. LB together with evaluation of expression of PD-1 ligand (PD-L1) can assess mutational load thus assisting in screening patients who may benefit from immunotherapy.

Metabolic imaging - current standard for detection of recurrent HNSCC

Increased metabolic activity detected in positron emission tomography-computed tomography (PET-CT) is currently the most sensitive technique to detect residual cancer or progression of HNSCC after curative treatment. High metabolically active tumor volume (MTV) is associated with treatment resistance and shows independent prognostic significance. While PET-CT shows excellent sensitivity, it may lead to false positive findings caused by inflammation or other conditions having increased cellular metabolic rate. Furthermore, metabolic imaging does not elucidate resistance mechanisms nor does it assist in planning of targeted treatments. Whether LB could assist or replace PET/CT in response monitoring and detection of recurrence remains thus far unknown.

Study objectives

i) To investigate whether MTV detected in PET-CT correlates to pattern and amount of genetic alterations in ctDNA of patients with HNSCC referred to radiotherapy (RT) or chemoradiotherapy (CRT) ii) To determine whether LB is more sensitive than PET/CT in detecting residual tumor three months after completion of RT or CRT iii) To evaluate exhaustive genetic landscape of patients with locally advanced HNSCC in order to characterize resistance or target genes for alternative treatments including (but not limited to) immunotherapy, antibodies against epidermal growth factor receptor (EGFR), and hypoxia- and virus-activated compounds iv) To validate a novel digital droplet polymerase chain reaction (PCR) technique for non-invasive surveillance of patients at high risk for recurrence of HNSCC