Prospective Study on Exemption of Tumor Bed Boost Radiotherapy for pCR Patients After Breast Conserving Surgery With Neoadjuvant Therapy

Inclusion Criteria: (1) Voluntary participation, good compliance, able to cooperate with the trial observation, and having signed a written informed consent form; (2) Confirmed as invasive cancer through pathological tissue examination, and received baseline breast MR or PET/MR examination before neoadjuvant therapy; (3) Received the standard neoadjuvant treatment plan recommended by the guidelines based on molecular typing; (4) Single lesion, initially diagnosed as cT1-3N0-3a; (5) Underwent breast-conserving surgery, with negative surgical margins and a margin distance of ≥1mm, and achieved pCR of the primary breast lesion after NAC (ypT0); (6) Age 30-75 years, ECOG score 0-1; (7) Met the basic requirements for adjuvant radiotherapy, including basically normal peripheral blood count, no significant abnormalities in heart, liver, and kidney functions, and basically normal electrocardiogram; (8) Had no previous chest radiotherapy. Exclusion Criteria: (1) Pregnant women, lactating women, or women with reproductive capacity but without contraceptive measures in place; (2) Known to carry mutated susceptibility genes for breast cancer (including BRCA-1 and BRCA-2); (3) Diagnosed with cT4, N3b-c, bilateral breast cancer, with multiple primary lesions, multicentricity or non-bulky enhancement at the primary site; (4) Not receiving the standard neoadjuvant treatment regimen recommended by guidelines, or the primary breast lesion did not achieve pCR (including ypTis) after NAC; (5) Suffering from other malignant tumors or participating in other clinical trials simultaneously; (6) Unable to start radiotherapy within 8 weeks after breast cancer surgery; (7) Diagnosed with distant metastasis through initial imaging or pathology; (8) Previous history of breast cancer, history of radiotherapy in the neck, chest or ipsilateral axilla; (9) Severe non-tumor-related medical comorbidities affecting the implementation of radiotherapy; (10) Suffering from uncontrollable neurological, mental disorders or mental impairments, with poor compliance and inability to cooperate and describe treatment responses.