Circulating tumour cell and cell-free DNA kinetics during radiotherapy in patients with intact head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) treatment response relies heavily on macroscopic clinical findings. Blood monitoring of circulating markers during treatment may improve earlier detection of responders versus non-responders during radiotherapy. In this study, patients with intact tumour of HNSCC were enrolled in the prospective PREDICT-HN study. Pre-, after first treatment, weekly, and post-treatment blood samples were collected. CTC was enumerated using the CellSearch system. cfDNA was quantified from cfNA isolated at pre-, mid- and post-treatment timepoints. Blood samples were collected from 45 patients. Of the 339 samples analysed for CTC, 31% had detectable CTCs. Nine patients had detectable CTCs (1-3/7.5ml blood) in pre-treatment samples. After 1 fraction, 16 patients had CTCs detected, with 12 who had no pre-treatment CTC. Sixteen (36%) patients had detectable CTC in final week of treatment. There was no correlation between cancer stage, nodal status and tumour burden with CTC. cfDNA levels increased during treatment, with its highest level in the final week and lowest at post-treatment. Our results showed in HNSCC that CTCs can be detected during radiotherapy, suggesting mobilization into circulation during treatment, with as-yet-unknown viability. cfDNA kinetics during treatment correlated with CTC release, and may indicate apoptotic change. Simple Summary Head and neck squamous cell carcinoma (HNSCC) treatment response relies heavily on macroscopic clinical findings. Blood monitoring of circulating markers such as circulating tumour cell (CTC) and cell-free DNA (cfDNA) during treatment may improve earlier detection of responders versus non-responders during definitive radiotherapy. Although the detection of CTCs and cfDNA in patients with HNSCC has been described, there is minimal data on the kinetics of CTC counts and cfDNA levels during radiotherapy in patients with HNSCC. Here, our study prospectively describes the changes in CTC and cfDNA enumeration during radiotherapy in patients with HNSCC. Our results showed, for the first time to our knowledge, in HNSCC, that CTCs can be detected during radiotherapy, suggesting mobilization into peripheral circulation during treatment, with as-yet-unknown viability. cfDNA kinetics during treatment correlated with CTC release, may indicate apoptotic change during radiotherapy. Combined cfDNA-CTC as an early marker of treatment response should be investigated further.