Omitting axillary lymph node dissection or not? A multicenter, retrospective study for breast cancer patients potentially eligible for abemaciclib since the SENOMAC trial.

[BACKGROUND] The SENOMAC trial has resolved the longstanding clinical debate regarding the omission of axillary lymph node dissection (ALND) in patients with 1–2 positive sentinel lymph nodes (SLNs). However, the MonarchE trial demonstrated the benefit of abemaciclib as an adjuvant endocrine therapy for high-risk patients with hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer. The inclusion criteria of MonarchE, particularly the requirement for pN2 status, may necessitate reconsideration of surgical interventions.

[METHODS] This study retrospectively included 711 patients with cT1-2N0M0, HR+/HER2-, and 1–2 positive SLNs in the Shanghai Jiao Tong University breast cancer database. All patients underwent further ALND. The study evaluated the proportion of patients with pathological stage upgrading to pN2 or pN3 after ALND, analyzed the independent predictors of high lymph node burden, and further evaluated the diagnostic efficacy of the SENOMAC nomogram in predicting high nodal burden.

[RESULTS] Among the 711 patients, 17.6% were confirmed to be at pN2 or pN3 stage by ALND, meeting the criteria for adjuvant abemaciclib treatment. Multivariate analysis showed that the number of positive SLNs (OR = 5.267, 95% CI: 3.487–7.958) and the number of removed SLNs (OR = 0.839, 95% CI: 0.752–0.927) and tumor size (OR = 2.409, 95% CI: 1.615–3.594) were independent risk factors for predicting pN2/pN3. Patients with pN2-pN3 disease had significantly worse recurrence-free survival compared to those with pN1 disease (HR = 4.958, 95% CI: 1.786–13.762,  = 0.0017). The predictive performance of the SENOMAC nomogram in this cohort was AUC = 0.763 (95% CI: 0.712–0.814).

[CONCLUSIONS] 17.6% of patients with 1–2 positive SLNs and no additional high-risk factors were reclassified as high nodal burden after ALND. Given the relatively low prevalence of these cases, routinely performing ALND on all such patients has limited clinical benefit.