Omission of Adjuvant Radiotherapy in Low- and Intermediate-Risk Ductal Carcinoma In Situ After Breast-Conserving Surgery

Inclusion criteria

• 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.

Exclusion criteria

• Known BRCA1 or BRCA2 germline mutation carriers (genetic testing not mandatory)；
• Contraindications to radiotherapy, including active connective tissue disease；
• Active infection requiring systemic treatment；
• Bilateral breast cancer or prior contralateral breast cancer；
• Severe uncontrolled comorbidities, including significant cardiac, pulmonary, hepatic, renal, hematologic, or psychiatric disorders；
• History of other malignancies, including thyroid cancer, except adequately treated basal cell carcinoma of the skin or cervical carcinoma in situ；
• Prior thoracic radiotherapy；
• Pregnant or breastfeeding patients；
• Estimated life expectancy ≤5 years；
• Poor compliance or inability to adhere to study follow-up requirements.