cN3c breast cancer with ipsilateral supraclavicular (SCV) lymph nodal (SCLN) metastasis is known to have a dismal prognosis. Currently, the combined-modality therapy consisting of primary systemic therapy (PST), subsequent local and/or systemic therapy based on response is the standard of care. However, the value of giving radiotherapy (RT) boost to SCV region remains uncertain in cN3c patients. This study aimed to assess the efficacy and safety of RT boost to the SCV area in high-risk cN3c breast cancer patients based on nodal response following PST.

This study is a phase II single-arm, prospective clinical trial aimed at assessing the efficacy and safety of RT boost to the SCV area among high-risk cN3c breast cancer patients contingent upon the nodal response after PST.

Our previous retrospective study revealed that nodal response to PST serves as an independent prognostic factor for survival and pattern of failure. A cumulative SCV dose of ≥60 Gy has been associated with improved overall survival (OS) in subgroup of patients who did not achieve SCLN cCR.

Based on nodal response to PST, patients will be categorized into three groups: those who did not achieve cCR in SCLN (considered high risk), those who achieved SCLN cCR but did not attain pCR in ALN (considered intermediate risk), and those who achieved cCR in SCLN and pCR in ALN (considered low risk). High-risk patients will undergo boost irradiation to the SCV with a cumulative dose of ≥60 Gy.

Inclusion Criteria:

• Voluntary participation with documented informed consent.
• Females aged ≥18 years.
• Histological or cytological confirmed primary breast carcinoma.
• Clinical diagnosis of cN3c.
• Receipt of neoadjuvant therapy, guided by the attending physician and current treatment guidelines.
• Did not achieve cCR in SCLN following neoadjuvant therapy.
• Undergoing curative-intent breast cancer surgery post-neoadjuvant therapy.
• Pathological evaluation of axillary lymph nodes post-surgery.
• KPS score ≥80, with expected survival exceeding 2 years.
• Complete healing of surgical incision without complications.
• Negative pathological surgical margins.
• Availability of hormonal receptor (ER/PR), HER2, and Ki-67 status for the primary breast lesion.
• Pre-menopausal females required to practice contraception for at least one month prior to screening, maintaining contraception throughout the study and for a specified period post-study cessation.

Exclusion Criteria:

• Patients with confirmed distant metastases by pathology or imaging.
• Those who have not received neoadjuvant systemic therapy.
• Patients who have not undergone curative-intent surgery.
• Pregnant or lactating women.
• Individuals with severe non-neoplastic comorbidities affecting radiotherapy implementation.
• History of malignancy within the past 5 years (excluding ductal carcinoma in situ, basal cell carcinoma, squamous cell carcinoma in situ, cervical carcinoma in situ, and in situ adenocarcinoma of the lung).
• Simultaneous contralateral breast cancer.
• History of prior radiation therapy to the neck, chest, or ipsilateral axilla.
• Active collagen vascular disease.
• Patients with T4 staging of the primary tumor.
• Inability to initiate radiotherapy within 12 weeks post breast cancer curative surgery (breast-conserving surgery or mastectomy), or within 8 weeks post completion of adjuvant chemotherapy.