Impact of Sentinel Node Omission in Early-Stage Breast Cancers on Adjuvant Therapy Decision-Making

BACKGROUND: Recent studies suggest that selective omission of sentinel lymph node biopsy (SLNB) in early-stage breast cancer may reduce morbidity without compromising oncologic outcomes. The impact of SLNB omission on eligibility for adjuvant therapies, including CDK4/6 inhibitors and partial breast irradiation (PBI), remains unclear, as both depend on nodal status. METHODS: Using a single-institution registry (2012-2024), we identified women with cT1N0, ER+/HER2-, grade 1-2 breast cancer who would have been candidates for SLNB omission. Pathologic nodal status and eligibility for CDK4/6 inhibitors and PBI were assessed. RESULTS: Among 1,194 patients, 130 (10.9%) had ≥1 positive sentinel lymph nodes, including five (0.4%) with ≥4 positive nodes. Nodal positivity decreased with age (18% <50 years vs. 7.4% ≥70 years (p < 0.001). Nodal positivity increased with tumor size (6.2% (cT1a), 6.6% (cT1b), 14.4% (cT1c); p < 0.001) and with tumor grade (8.5% (grade 1) vs. 12.4% (grade 2); p = 0.03). In women aged 50-59 years with cT1a/b tumors, nodal positivity did not differ by grade (6.8% grade 1 vs. 11.1% grade 2; p = 0.43). In women aged ≥60 years with cT1a/b tumors, rates were 3.1 and 2.1%, respectively (p = 1.00). CONCLUSIONS: Under current guidelines, SLNB omission would have excluded 18% of women <50 and 8.8% of women ≥50 from consideration for CDK4/6 inhibitors and PBI. Sentinel lymph node biopsy omission is unlikely to affect adjuvant treatment selection in carefully selected older women with small, low-grade tumors, particularly those aged ≥60 years with grade 1 cT1a/b disease, in whom occult nodal positivity was only 2.1%. In contrast, younger patients, those with cT1c tumors, and those with higher-grade disease demonstrated substantially higher rates of nodal involvement, suggesting that SLNB continues to provide clinically actionable information that may influence eligibility for CDK4/6 inhibitors and partial breast irradiation. These findings support a risk-adapted rather than universal approach to SLNB omission.