Non-sentinel Lymph Node Metastatic Burden in Patients Undergoing Mastectomy With One or Two Positive Sentinel Lymph Nodes: Implications of Omitting Axillary Lymph Node Dissection

BackgroundOmission of axillary lymph node dissection (ALND) is increasingly accepted for patients with a limited number of metastatic sentinel lymph nodes (SLNs), and this approach is now being extended to patients treated with mastectomy.After mastectomy, however, the total number of metastatic axillary nodes still informs adjuvant chemotherapy, cyclin-dependent kinase 4/6 (CDK4/6) inhibitor eligibility, and radiotherapy field design, and this information is lost when ALND is omitted.This exploratory, descriptive study quantified the non-SLN metastatic burden that would have remained undetected had ALND been omitted in mastectomy patients at our institution. MethodologyWe retrospectively reviewed patients with clinically node-negative breast cancer who underwent SLN biopsy followed by completion ALND for a positive SLN at Kanazawa University Hospital between January 2022 and April 2026.Patients treated with neoadjuvant chemotherapy or breast-conserving surgery were excluded.Patients with one or two positive SLNs were defined as the ALND-omission candidate group.The primary endpoint was the proportion of candidates with four or more metastatic axillary nodes in total (SLNs plus non-SLNs; pathological nodal stage 2 (pN2) or higher).Secondary endpoints were the proportion of candidates with any non-SLN metastasis and the proportion with four or more non-SLN metastases; these were compared between patients with one and two positive SLNs.95% confidence intervals (CIs) were calculated by the Clopper-Pearson method, and proportions were compared with Fisher's exact test.No multivariable or predictive modeling was performed. ResultsTwenty-seven patients were analyzed (median age 53 years, range 41-79; total mastectomy 25, skin-sparing mastectomy 1, nipple-sparing converted to skin-sparing mastectomy 1).Twenty-six tumors (96.3%) were luminal type.The omission candidate group comprised 21 patients (77.8%): 17 with one positive SLN and four with two positive SLNs.Four or more total positive nodes (pN2 or higher) were found in seven of 21 candidates (33.3%; 95% CI 14.6-57.0%),any non-SLN metastasis in 11 (52.4%;95% CI 29.8-74.3%),and four or more non-SLN metastases in five (23.8%; 95% CI 8.2-47.2%).pN2 or higher disease was found in four of 17 patients (23.5%) with one positive SLN and in three of four (75.0%) with two positive SLNs (P = 0.088); four or more non-SLN metastases were found in 11.8% versus 75.0%(P = 0.028).Four of the seven pN2-orhigher patients had invasive lobular carcinoma, and three had primary tumors larger than 80 mm. ConclusionsIn this small single-center mastectomy cohort, omitting ALND for one or two positive SLNs would have left non-SLN metastases undetected in about half of patients and would have understaged roughly one-third as pN1 rather than pN2 or higher.A high nodal burden was observed more often with two positive SLNs than with one, although the two-SLN subgroup was very small and this observation is hypothesis-generating.Because pN stage still informs adjuvant decisions after mastectomy, these data suggest that ALND omission in this setting should be accompanied by careful patient selection and a predefined adjuvant strategy; prospective studies with outcome data are needed to define that strategy.