Reconciling Sentinel Node Omission with CDK4/6 Inhibitor Eligibility in HR+/HER2- Early Breast Cancer: A Real-World Cohort Analysis.

[PURPOSE] Omission of sentinel lymph node biopsy (SLNB) in selected hormone receptor-positive (HR+), HER2-negative (HER2-) early breast cancer patients has demonstrated safety in prospective trials. However, accurate axillary staging remains important for identifying candidates for adjuvant CDK4/6 inhibitor therapy. We quantified the impact of SLNB omission on CDK4/6 eligibility and explored predictors of occult nodal disease in a real-world cohort.

[METHODS] We retrospectively analyzed 948 patients treated 2014 to 2022 at Tübingen University Hospital who met criteria proposed for potential SLNB omission: age ≥ 50 years, cT1 cN0, HR+/HER2-, grade 1 to 2 tumors treated with breast-conserving surgery and whole-breast irradiation. We assessed the prevalence of occult nodal metastases and potential eligibility for adjuvant abemaciclib (monarchE-criteria) or ribociclib (NATALEE-criteria) based on final pathology and fitted multivariable logistic models.

[RESULTS] Among 948 patients meeting SLNB omission criteria, 143 (15.1%) harbored occult nodal disease. Of these node-positive patients, 17 fulfilled the criteria for abemaciclib eligibility. For ribociclib, 105 node-positive patients were eligible. On multivariable analysis, multifocality (OR = 2.3; P ≤ .001) and cT1c tumor stage (OR = 1.76; P = .008) predicted axillary upstaging; invasive lobular carcinoma (ILC) showed higher crude upstaging than IDC/NST (22.6% vs. 14.0%) but did not retain independent significance after adjustment.

[CONCLUSIONS] Omitting sentinel node biopsy in selected patients leads to under-detection of nodal metastasis in a relevant proportion of patients, particularly with cT1c tumors, multi-focal tumors and ILC. As these patients may benefit from more intensive adjuvant treatment, omission of sentinel-node biopsy should be part of decision-making. Future trials should investigate the impact of adjuvant treatment for patients with occult lymph node metastases.