Prediction of Residual Disease by Circulating DNA Detection After Potentiated Radiotherapy for Locally Advanced Head and Neck Cancer

Sixty percent of newly diagnosed head and neck squamous cell carcinomas (HNSCCs) are at a locally advanced (LA) stage. Depending on tumor site, stage, and resectability, locoregional failure rates can range from 35% to 65%. The persistence of residual disease at the end of treatment is a major prognostic element but is not always reliably assessed by current imaging techniques. Up to 40-50% of patients have residual adenomegaly and only 30% have viable disease when further adenectomy is performed. Sensitive and reproducible detection of residual disease after treatment is a major challenge in this patient category. 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET/CT) guided surveillance, with a negative predictive value of 95-97%, has proven to be non-inferior to cervical curage in HNSCCs with residual adenomegaly. Cervical curage is now indicated only if the response assessed by PET-CT is incomplete. Nevertheless, the ability of PET-CT to predict treatment failure is unsatisfactory due to a high frequency of false positives, because of inflammatory changes, with a positive predictive value of about 20-50%. Circulating tumor DNA (ctDNA) may provide a more reliable assessment of response to potentiated radiotherapy. Liquid biopsy monitoring of response in patients treated with potentiated radiation therapy for locally advanced HNSCCs a has been shown to be feasible. In 85% of patients, ctDNA is detectable and correlates significantly with tumor volume and response to treatment. In addition, one study showed that post-radiotherapy analysis of circulating HPV16 viral DNA (cvDNA) in patients with HPV16-related HNSCCs complemented PET-CT and helped guide management decisions. HPV16 cvDNA and PET-CT have similar negative predictive values, whereas the positive predictive value is higher for HPV16 cvDNA (100% versus 50%). Nevertheless, current data are insufficient to allow routine use of this marker. This is a multicenter, single arm, open study for patients with a locally advanced head and neck cancer for which a potentiated radiotherapy is indicated.