Phase III, prospective, interventional, multicentric, comparative, randomized, open study with 2 parallel arms, evaluating the efficacy of Cicaderma ointment vs standard management of each site in preventing the onset of grade > 2 radiodermatitis according to the National Cancer Institute - Common Terminology Criteria for Adverse Events-Version (NCI-CTCAE-V5)

Breast cancer is the most common cancer in women. It accounts for more than 1/3 of new cancer cases and is the 1st cause of death for women.

Management usually includes tumorectomy or mastectomy precede or not by a chemotherapy, then adjuvant irradiation that can be supplemented with adjuvant chemotherapy and / or hormone therapy.

Radiotherapy uses ionizing radiation (photons, electrons ...) to destroy cancer cells and consists in precisely directing these radiations on the area to be treated while preserving as much as possible healthy tissues and surrounding organs.

Radiation-induced dermatitis is a skin lesion that occurs after exposure to ionizing radiation and is commonly seen in patients. Acute radiodermatitis occurs in the days or weeks following the start of irradiation with different degrees of severity (dry or exsudative radiodermatitis, acute radionecrosis) They are responsible for an alteration of patients' quality of life (pain, sensitivity to UV radiation, discomfort sensations ...), which may lead to a temporary or even permanent therapeutic interruption and reduce the probability of tumor control.

The management of these dermatitis is very heterogeneous, no study having demonstrated the superiority of a preventive or curative treatment. Trolamine (Biafine®) is to date the only topic with a Marketing Authorization (MA) for the treatment of radiation-induced secondary erythema.

A study conducted on 254 patients at the Léon Bérard Center from 1999 to 2001 demonstrated that the preventive use of a calendula-based topical was associated with a statistically significant reduction of grade 2 radiodermitis compared to trolamine in patients presenting an early breast cancer treated with post-operative irradiation. However, this calendula ointment, which does not have the MA in the indicated indication, was in practice more difficult to apply than trolamine.

Currently, skin hygiene measures to be applied are systematically explained to patients before carrying out post-operative radiotherapy (cotton clothing, neutral soap, etc.). Some centers such as Center Léon Bérard recommend the systematic use of a topic after each session, while others recommend hygiene measures or implement other options (essential oils ...). However, the effectiveness of these current practices on the prevention of radiodermatitis has not yet been demonstrated.

It is a phase III, prospective, interventional, multicentric, comparative, randomized, open study with 2 parallel arms Patients will be randomized (1 :1) in Arm A (hygiene measures + preventive treatment with Cicaderma ointment) or Arm B (preventive treatment according to the site recommendations (at least the hygiene measures) with a stratification (site, body mass index ≤25 vs >25 and RT hypofractionning).

Inclusion Criteria:

• Age ≥18 years
• Patient requiring a post-operative radiotherapy (post mastectomy or tumorectomy) for a mammary adenocarcinoma or an unilateral in situ breast cancer histologically documented, early stage of disease (non metastatic)
• Patient with no residual tumor (R0 or R1)
• Patient informed and having given her signed consent
• Patient affiliated to a social security regimen

Exclusion Criteria:

• Unsolved cutaneous toxicities of any previous treatment
• Hormonotherapy started prior to radiotherapy
• Concomitant use of other topical treatments than the study treatments on the irradiated area
• Patient treated by concomitant chemotherapy and/or targeted therapy
• Known hypersensibility to at least one component of the topicals used or Cicadema ointment
• Patient for whom follow-up does not seem possible even in the short term
• Pregnant or breastfeeding woman
• Participation in another clinical trial that may interfere with the evaluation of the primary endpoint
• Patient Under tutorship or curatorship or deprived of liberty