A Prospective, Multicenter, Randomized Phase III Non-Inferiority Trial Evaluating Omission of Adjuvant Radiotherapy in Low- and Intermediate-Risk ER-Positive HER2-Negative Ductal Carcinoma In Situ Following Breast-Conserving Surgery
This is a prospective, multicenter, randomized, open-label, phase III non-inferiority trial designed to evaluate whether omission of postoperative radiotherapy is clinically acceptable in patients with low- and intermediate-risk ductal carcinoma in situ (DCIS) following breast-conserving surgery. Eligible patients include women aged ≥40 years with ER-positive, low- or intermediate-grade DCIS, tumor size ≤2.5 cm, negative surgical margins ≥3 mm, absence of comedo necrosis, and screen-detected unifocal disease. Patients will be randomized to postoperative observation alone or adjuvant radiotherapy. The primary endpoint is 5-year ipsilateral breast tumor recurrence (IBTR).
• Female patients aged ≥40 years；
• Histologically confirmed low- or intermediate-grade ductal carcinoma in situ (DCIS) without invasive carcinoma, including incidental DCIS identified within benign breast lesions；
• Tumor size ≤2.5 cm on final pathology；
• Negative surgical margins ≥3 mm, including margins obtained after re-excision；
• Estrogen receptor-positive disease (ER ≥10%) with planned endocrine therapy using tamoxifen；
• Unifocal lesion；
• Absence of comedo necrosis；
• Screen-detected disease without bloody nipple discharge or palpable mass；
• Clinically node-negative disease；
⁃ Patients randomized to the radiotherapy arm must initiate radiotherapy within 3 months after surgery；
⁃ Central pathology review by the participating institution required；
⁃ Ability to understand and willingness to sign written informed consent.