Abstract 456: Circulating tumor cells and cfDNA changes during radiotherapy in patients with head and neck cancer
Authors: Ng Sweet Ping , Hall Carolyn S. , Meas Salyna , Sarli Vanessa N. , Bahig Houda , Elgohari Baher , Moreno Amy , Skinner Heath D. , Garden Adam S. , Rosenthal David I. , Morrison William H. , Phan Jack , Gunn G Brandon , Frank Steven J. , Fuller Clifton D. , Lucci Anthony 
Published: August 2019

Introduction: Head and neck cancer treatment response relies heavily on macroscopic clinical findings. Blood monitoring of circulating markers such as circulating tumor cell (CTC) and cell-free DNA (cfDNA) during treatment may improve earlier detection of responders versus non-responders during definitive radiotherapy. Our work prospectively describes the changes in CTC and cfDNA enumeration during definitive radiotherapy.

Methods: Patients with mucosal head and neck squamous cell carcinoma and intact gross tumor were eligible for the prospective IRB-approved PREDICT-HN study. Blood samples were collected pre-treatment, after first treatment, weekly, and post-treatment (CellSave and EDTA tubes). CTC was enumerated using the FDA-approved CellSearch (Menarini Silicon Biosystems) system. Filtered plasma were collected from the EDTA tubes and stored at -80C. cfNA from pre-, mid- and post-treatment timepoints were isolated from the filtered plasma using the MagMAX Nucleic Acid Isolation Kit (Thermo Fisher Scientific) and cfDNA were quantified with Qubit high sensitivity dsDNA assay (Invitrogen).

Results: 339 blood samples were collected from 45 patients; 137 had detectable CTC. Eight patients had detectable CTCs (1-3/7.5ml blood) in pre-treatment samples. After 1 fraction of radiotherapy, 16 patients had CTCs detected with 12 who had no CTC detected pre-treatment. 19 (42%) patients had detectable CTC in week 6 of treatment. All patients had detectable CTC at some point during radiotherapy except for one patient who had no CTC detected pre, during and post-treatment. There was no correlation between cancer stage, nodal status and gross tumor volume with detection of CTC. Overall circulating cfDNA levels increased during treatment, with their highest level in the final week of treatment similar to when the majority of CTC were detectable in patients, and lowest at the post-treatment time-point.

Conclusions: Our interim results showed, for the 1sttime, to our knowledge, that CTCs can be detected during radiotherapy of head and neck cancer, 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.

Citation Format: Sweet Ping Ng, Carolyn S. Hall, Salyna Meas, Vanessa N. Sarli, Houda Bahig, Baher Elgohari, Amy Moreno, Heath D. Skinner, Adam S. Garden, David I. Rosenthal, William H. Morrison, Jack Phan, G Brandon Gunn, Steven J. Frank, Clifton D. Fuller, Anthony Lucci. Circulating tumor cells and cfDNA changes during radiotherapy in patients with head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 456.