The need to tailor the omission of axillary lymph node dissection to patients with good prognosis and sentinel node micro‐metastases

BACKGROUND: Results of IBCSG‐23‐01‐trial which included breast cancer patients with involved sentinel nodes (SN) by isolated‐tumor‐cells or micro‐metastases supported the non‐inferiority of completion axillary‐lymph‐node‐dissection (cALND) omission. However, current data are considered insufficient to avoid cALND for all patients with SN‐micro‐metastases. METHODS: To investigate the impact of cALND omission on disease‐free‐survival (DFS) and overall survival (OS), we analyzed a cohort of 1421 patients <75 years old with SN‐micro‐metastases who underwent breast conservative surgery (BCS). We used inverse probability of treatment weighting (IPTW) to obtain adjusted Kaplan–Meier estimators representing the experience in the analysis cohort, based on whether all or none had been subject to cALND omission. RESULTS: Weighted log‐rank tests comparing adjusted Kaplan–Meier survival curves showed significant differences in OS (p‐value = 0.002) and borderline significant differences in DFS (p‐value = 0.090) between cALND omission versus cALND. Cox's regression using stabilized IPTW evidenced an average increase in the risk of death associated with cALND omission (HR = 2.77, CI95% = 1.36–5.66). Subgroup analyses suggest that the rates of recurrence and death associated with cALND omission increase substantially after a large period of time in the half sample of women less likely to miss cALND. CONCLUSIONS: Using IPTW to estimate the causal treatment effect of cALND in a large retrospective cohort, we concluded cALND omission is associated with an increased risk of recurrence and death in women of <75 years old treated by BCS in the absence of a large consensus in favor of omitting cALND. These results are particularly contributive for patients treated by BCS where cALND omission rates increase over time.