This clinical trial is testing a new skin gel called GR1014-CG to evaluate its safety and see if it can help prevent or reduce skin irritation (such as redness, soreness, etc.) caused by radiation therapy (RT) after breast-conserving surgery for early-stage breast cancer. The study is for women aged 18 and older who have had surgery to remove a breast tumor and need radiation therapy.

The main goals of the study are to find out:

• If GR1014-CG is safe to use
• If the gel can prevent or lower the severity of skin irritation caused by RT.

During the study participants will,

• Be randomly assigned to use one of two strengths of GR1014-CG (4.7% or 2.4%) or a placebo gel (a gel with no active drug).
• Apply the gel to the breast before each radiation session for 5 days.
• Visit the clinic once a week for 4 weeks to check their skin and overall health. At the end of the 4th week, if there are still signs of irritation participants will come to the clinic for a checkup 2 weeks after, and then again 2 weeks after if the irritation is still observed.
• Keep a diary to record any pain or itching they may feel.

Adjuvant radiation therapy (RT) decreases the chances of local cancer reappearance and improves survival rates. However, radiotherapy is often associated with side effects, including radiation-induced dermatitis (radiodermatitis). Symptoms of radiation-induced dermatitis include skin redness (erythema), swelling (oedema), dry or moist peeling of the skin (desquamation), and varying degrees of pain. GR1014 cutaneous gel (GR1014-CG) contains amifostine thiol (GR1014), an active substance with well-established radioprotective effects. The protective properties of GR1014-CG are potentially beneficial in preventing radiodermatitis, particularly in patients with breast cancer treated with adjuvant RT. GR1014 CG is designed to be topically applied to the skin before each RT session without any modifications to the planned course of RT.

This is a dose-finding, phase-2 trial to investigate the safety, tolerability, and efficacy of GR1014-CG as a topical radioprotector in the reduction of radiodermatitis occurring in patients treated with adjuvant ultra-hypofractionated RT (26 Gy in 5 fractions over 1 week) for localized, non-metastatic breast cancer after tumor removal (lumpectomy) versus vehicle gel.

Inclusion Criteria:

• Female patients with age ≥18 years. Those of childbearing potential must be using highly effective contraception methods during the study and for 30 days after the last administration of the study treatment and have a negative pregnancy test at screening and no more than 10 days prior to the administration of the first dose of study treatment
• Patients with primary, localized breast cancer without metastases pTis, T1-3, pN0-N1mi, M0, who have undergone breast-conserving surgical excision and require adjuvant RT. The patients should be randomized after having recovered from the last surgery and, if delivered, the adjuvant chemotherapy. The patients can be included no matter the status of estrogen and progesterone receptors, malignancy grade, or HER2 status.
• ECOG performance status 0-2
• Patients to be treated with ultra hypofractionated RT, 26 Gy in 5 fractions (5.2 Gy) on whole breast (EQD2 > 42.6 Gy for α/β of 3)
• Patients with no signs of dermatitis in the breast area to be irradiated, i.e., assessed Grade 0 as per CTCAE radiation dermatitis grading
• Patients whom the investigator has deemed able to comply with the RT and investigational treatment done under the supervision of the medical personnel throughout the study period
• Patients who have completed the appropriate washout period for any prior interventions or treatments

Exclusion Criteria:

• Pregnant and breastfeeding women
• Patients under any treatment concomitant to radiotherapy tested in another clinical study
• Allergies to any of the ingredients in GR1014-CG
• Patients protected by law (legal guardianship or protection)
• Patients unable to adhere to the requirements of the study
• History of thoracic RT
• Participants with the presence of skin rash, ulceration, unhealed surgical wounds, biopsy sites, or open wound in the breast or chest area at visit 2
• Patients suffering from scleroderma, auto-immune disease, micro-vascular diseases, collagen tissue diseases, lupus, pre-existing loss of skin integrity, active eczema in the region to be treated or with a history of any of the following: drug-induced severe cutaneous adverse reaction (SCAR; including, but not limited to Stevens-Johnson syndrome/toxic epidermal necrolysis [SJS/TEN], or drug reaction with eosinophilia and systemic symptoms)