Locally advanced head and neck squamous cell carcinoma (LAHNSCC) is a heterogeneous disease, associated with a poor prognosis and no improvement in overall survival for years. Furthermore, treatments (surgery, radiotherapy, chemotherapy) are frequently associated with acute and late toxicities. Beside p16/HPV + tumors, only TNM classification can help estimating the prognosis of the patients. A better evaluation of the prognosis and of the risk of metastatic spread would help defining the best treatment.

Circulating tumor DNA (ctDNA) has been reported as both a prognostic factor and a non-invasive way to assess tumor relapse in several cancer types. Few data are available in HNSCC, and no data among p16/HPV- cancers. Indeed, ctDNA assessment is usually based on tumor mutation monitoring. But if recurrent mutations are frequent in several cancers types (PIK3CA, KRAS, ESR1, TERT…), there is no recurrent mutation observed in HNSCC. Thus ctDNA assessment in LAHNSCC must be performed after the identification of a tumor specific mutation for each patient.

In that context, the aim of this study is to perform a molecular analysis of primary LAHNSCC, and to look for the amount of ctDNA before surgery, after surgery, and during 18 months of follow up.

The patients will be enrolled before surgery and follow-up during 18 months. During patient participation, 20 ml of blood will be collected 7 times (before and after surgery, 6 months after diagnosis and every 3 months thereafter until 18 months of follow up).

Mutation analysis on tumor and healthy tissue will be performed on primary tumors and lymph node dissection, after removal by the surgeon.

Circulating tumor DNA will be detected on blood sample

Inclusion Criteria:

• Operable Head and neck squamous cell carcinoma (T3-T4 stage and/or N+)
• No p16 expression
• Curative treatment proposed based on surgery + radiotherapy (+/- chemotherapy)
• PS<3
• Written consent signed

Exclusion Criteria:

• Metastatic spread
• Previous radiotherapy of head or neck
• Previous HNSCC (except carcinoma restricted to glottis, with a surgery treatment alone and >3 years of follow up without relapse)