The necessity of sentinel lymph node biopsy (SLNB) in early-stage, node-negative (cN0) breast cancer is increasingly questioned in the era of surgical de-escalation and biologically driven treatment strategies. While SLNB has long replaced axillary lymph node dissection to reduce morbidity, it nevertheless carries a measurable risk of complications, including lymphedema, pain, and reduced arm mobility. Recent high-quality evidence suggests that SLNB may be safely omitted in selected patients without compromising oncologic outcomes.

The SOUND randomized trial demonstrated that omission of SLNB in women with cT1N0, ultrasound-negative axilla treated with breast-conserving surgery (BCS) and whole-breast irradiation yields non-inferior 5-year distant disease-free survival, with axillary recurrence up to 1%. These findings were reinforced by the large INSEMA randomized trial, which included more than 5,000 cT1–2N0 patients and confirmed that SLNB omission does not adversely affect invasive disease-free survival or overall survival (non inferiority study). INSEMA, as SOUND, predominantly included women older than 50 years and postmenopausal, with approximately 90% of patients presenting with cT1N0 tumor. Importantly, INSEMA showed consistent and clinically significant improvements in patient-reported outcomes, including lower rates of chronic arm morbidity and lymphedema. Then the BOOG 2013-08 trial highlighted quality-of-life benefits at three years for patients who avoided SLNB.

However, caution is warranted for underrepresented subgroups such as HER2-positive, triple-negative, high-grade, or lobular cancers. Plus, the rate of macrometastatic sentinel lymph nodes was under 10% for cT1N0 patients but was around 20% for cT2N0 patients.

Collectively, these data support a paradigm shift toward selective axillary staging, emphasizing tumor biology, imaging accuracy, and systemic therapy over routine surgical assessment. Evidence indicates that SLNB omission is oncologically safe and functionally advantageous in Luminal cT1N0 patients.