Overview
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).
Eligibility
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.
