The impact of axillary lymph-node dissection omission on adjuvant abemaciclib eligibility in HR-positive, HER2-negative breast cancer with positive sentinel lymph nodes.

Background: The MonarchE trial demonstrated the additional benefit of abemaciclib as an adjuvant endocrine therapy for high-risk patients with hormone receptor (HR)-positive HER2-negative breast cancer. Meanwhile, the ACOSOG Z0011 trial established the omission of axillary lymph-node dissection (ALND) as a standard practice in certain patients with positive sentinel lymph-node biopsy (SNB). However, as the MonarchE eligibility criteria include the presence of four or more lymph-node metastases, omitting ALND may hinder the assessment of abemaciclib eligibility in some cases.

Methods: The study population consisted of patients with clinically node-negative, HR-positive, HER2-negative breast cancer who underwent SNB at our institution between January 2008 and December 2021. The proportion of patients meeting the MonarchE cohort1 criteria, and the potential impact of ALND omission on abemaciclib eligibility were assessed.

Results: Among the 1537 patients, 189 underwent SNB followed by ALND due to the presence of one or more positive sentinel nodes. Of these, 69 (36.5%) were eligible for abemaciclib. Eligibility was uncertain without ALND in 138 patients. Among the 138 patients, 124 were candidates for ALND omission, including 11 who were found to have four or more metastatic lymph nodes after completing ALND.

Conclusions: A few cases were identified in which abemaciclib eligibility was not properly determined due to ALND omission. This suggests that omitting ALND following SNB, when two of fewer positive nodes are detected, may not significantly impact the determination of abemaciclib eligibility.