The goal of this clinical trial is to evaluate a strategy integrating adjuvant radiation therapy versus strategy based on monitoring in the treatment of carcinomas spinocellular with high risk of recurrence (SCC).

The investigators will compare the disease-free survival (DFS) of patients treated with adjuvant radiation therapy versus surveillance in high risk of recurrence SCC.

The main question it aims to answer is:

Is DFS different between the "adjuvant radiotherapy" group and the "surveillance" group?

Participants will:

• be distributed in one of the two arms
• will be followed up every 4 months for 2 years, then every 6 months (clinical examination, identification of concomitant treatments, imaging, quality-of-life questionnaire)
• followed up until their death or their progression whether local, regional or metastatic

The use of adjuvant radiotherapy appears to provide clinical benefit, both theoretically and based on available retrospective data. This is why some patients already benefit from this complementary treatment. However, given the lack of prospective data, the use of adjuvant radiotherapy is based on heterogeneous criteria, depending on the choice of the clinician in charge of the patient or the habits of his institution.

The sponsor team therefore propose to conduct a national prospective study to compare the efficacy and safety of a strategy integrating adjuvant radiotherapy versus a strategy based on surveillance in patients with SCC at high risk of recurrence.

Considering that there is no validated standard after surgery for patients with a high risk of recurrence, it is not possible to determine a standard arm and an experimental arm. This study therefore falls within the framework of a Research Involving the Human Person of Category 2.

This protocol constitutes the first prospective evaluation of adjuvant radiotherapy, within the framework of a comparative study. This study will thus make it possible to avoid the use of this therapeutic alternative, without rigorous evaluation in a prospective framework. Its robust methodology will make it possible to determine whether adjuvant radiotherapy provides a clinical benefit to patients at high risk of recurrence. It will modify the standards of care for this patient population.

Inclusion Criteria:

I1. Patients aged ≥ 18 years at the time of signing the informed consent form; I2. Patients with histologically confirmed localized cutaneous squamous cell carcinoma;

Note: Patients with carcinoma of the external auditory canal may be included in the study;

I3. Patients treated with complete surgical excision (R0), regardless of the margin (submillimeter or supramillimeter);

I4. Disease with a high risk of recurrence defined by one of the following scenarios:

• presence of microscopic EPN without any other risk factors;
• presence of microscopic EPN with a single other risk factor;
• presence of 2 risk factors other than microscopic EPN;
• presence of 3 risk factors other than microscopic EPN;

Note: The risk factors considered are immunosuppression (limited to untreated hematologic disease), a tumor diameter >20 mm (longest axis, measured preferably clinically, or, failing that, histologically), a specific location (lip/ear/temple), deep invasion (tumor thickness >6 mm (Breslow) or invasion beyond the subcutaneous fat), poor differentiation, or desmoplasia;

I5. Patient informed and having signed a consent form to participate in the study; I6. Patient enrolled in a health insurance plan (or beneficiary of such a plan).

Exclusion Criteria:

NI1. Patients with in situ or mixed CEC; NI2. History of CEC with a high risk of recurrence in the same lymphatic drainage area (head and neck, trunk, or limb) within 2 years prior to the randomization date; NI3. History of CEC treated with systemic therapy; NI4. Patients with SCC localized to the endonasal, intraoral, anogenital, or vulvar mucosa;

NI5. Patients with recurrent SCC or SCC at very high risk of recurrence defined by one of the following criteria:

• EPN with ≥ 2 other risk factors,
• > 3 risk factors,
• bone invasion,
• immunosuppression due to immunosuppressive treatments (regardless of the reason). NI6. Patients with CEC presenting a single risk factor other than EPN; NI7. Patient with CEC and lymph node or distant metastasis; NI8. Patient with a history of cancer undergoing systemic and/or locoregional anticancer treatment;

Note: Local treatment of cutaneous keratoses with fluoropyrimidines is permitted outside the theoretical radiation field);

NI9. Patient with a contraindication to radiation therapy; NI10. Patient with a history of radiation therapy to the site of the lesion; NI11. Participation in another clinical trial that may interfere with the assessment of the primary endpoint; NI12. Patient under legal guardianship or conservatorship, or deprived of liberty; NI13. Pregnant or breastfeeding woman.