Acute radiation dermatitis (ARD) is the most common treatment-related adverse reaction following radiotherapy after modified radical mastectomy and/or prosthetic breast reconstruction in breast cancer patients. Moderate-to-severe ARD may compromise cosmetic outcomes and quality of life, and even impair radiotherapy efficacy. Current pharmacological prophylactic measures clinically employed - including topical corticosteroids, superoxide dismutase, and trolamine cream - demonstrate suboptimal efficacy and lack high-level evidence-based medical support. Emerging research indicates an association between cutaneous microbial homeostasis and ARD development, suggesting that maintaining skin surface acidity and modulating microecological balance may represent more effective preventive strategies.

This study evaluates the efficacy and safety of a natural weak-acid macromolecular/small molecular repair cream in preventing ARD among post-operative breast cancer patients receiving radiotherapy through skin microbiome modulation. We enrolled 326 high-risk early-stage breast cancer patients scheduled for post-operative radiotherapy and randomized them to compare the superiority of the natural weak-acid repair cream versus conventional care with moisturizer. Concurrent skin microbiome sampling was performed to assess microecological changes and their impact on ARD development. The findings will provide high-level clinical evidence and theoretical basis for the safer and more effective application of this natural weak-acid repair cream in preventing post-radiotherapy ARD in breast cancer patients.

Inclusion Criteria:

• Age ≥18 and <70 years, with pathologically confirmed breast cancer;

  • TNM stage T1-3N1-3M0 or T3-4N0M0;

    • Underwent mastectomy with or without implant reconstruction; ④ Medically fit for adjuvant radiotherapy (i.e., in good general condition to tolerate expected side effects such as fatigue, nausea, or vomiting); ⑤ No concurrent use of other skincare products throughout the study period;

      • Voluntary participation with signed informed consent, agreeing to comply with investigator-directed use of the trial product.

Exclusion Criteria:

• Prior history of radiotherapy;

  • Severe systemic diseases (e.g., significant cardiac, hepatic, or renal dysfunction; immunocompromising conditions such as lymphoma, acquired immunodeficiency syndrome [AIDS], or Wiskott-Aldrich syndrome) or history of other malignancies; ③ Skin reactions due to systemic therapies (e.g., chemotherapy, immunotherapy) or active dermatologic conditions in the treatment area;

    • Known hypersensitivity to the natural weak-acid macromolecular/small molecular repair cream or any of its components; ⑤ Current participation in other clinical trials or participation within the past 3 months, or judged by investigators to have poor compliance that would prevent completion of the study.