Radiotherapy and Long-term Outcomes in Early Breast Cancer With SLNB Omission

A Prospective Cohort Study of Radiotherapy Characteristics and Long-term Outcomes in Early Breast Cancer Omitting Sentinel Lymph Node Biopsy: The APROOB Cohort Study

This prospective, multicenter observational cohort study evaluates long-term outcomes in patients with early-stage invasive breast cancer who undergo breast-conserving surgery without sentinel lymph node biopsy or other axillary surgery and subsequently receive adjuvant radiotherapy.

The study will evaluate recurrence, survival, radiotherapy-related toxicities, and quality of life. Radiotherapy will be delivered according to routine clinical practice at each participating institution without protocol-mandated treatment assignment. Detailed radiotherapy characteristics, including treatment volume, technique, dose and fractionation, tumor-bed boost, and radiation dose to axillary lymph node levels I-III, will be prospectively collected to evaluate their associations with clinical outcomes.

Recent clinical trials have supported the omission of sentinel lymph node biopsy in selected patients with clinically node-negative early breast cancer. However, radiotherapy approaches after sentinel lymph node biopsy omission vary in routine clinical practice, and prospective data regarding the relationship between radiotherapy characteristics, radiation dose delivered to the axillary lymph nodes, and long-term clinical outcomes remain limited. Depending on patient and tumor characteristics and institutional practice, radiotherapy may include whole-breast or partial-breast irradiation with different treatment techniques, dose-fractionation schedules, and tumor-bed boost strategies. The APROOB Cohort is designed to prospectively characterize these variations and evaluate their associations with recurrence, survival, treatment-related toxicity, and quality of life following omission of sentinel lymph node biopsy. No radiotherapy technique, treatment volume, dose, or fractionation schedule is assigned by the study.

Inclusion Criteria:

• Female patients aged 19 years or older with histologically confirmed invasive breast cancer
• Patients who have undergone breast-conserving surgery with curative intent
• Patients who did not undergo axillary lymph node surgery, including sentinel lymph node biopsy, at the time of breast cancer surgery
• No evidence of distant metastasis on clinical and imaging evaluation before surgery
• Planned to receive adjuvant radiotherapy after breast-conserving surgery
• Ability and willingness to provide written informed consent before study participation

Exclusion Criteria:

• Patients initially diagnosed with breast carcinoma in situ before surgery who did not undergo sentinel lymph node biopsy but were subsequently found to have invasive breast cancer on final surgical pathology
• Receipt of neoadjuvant systemic therapy before breast cancer surgery
• History of a malignancy other than breast cancer within 5 years before study enrollment, except adequately treated non-melanoma skin cancer or carcinoma in situ other than breast carcinoma in situ
• Recurrent breast cancer
• Bilateral breast cancer or inflammatory breast cancer
• Prior radiotherapy to the ipsilateral breast or chest region
• Patients considered by the investigator to be unsuitable for study participation or long-term follow-up