Adherence Rate to Alliance for Clinical Trials in Oncology Z0011 Trial Based on Breast Cancer Subtype.

INTRODUCTION: ACOSOG Z0011 trial (Z11) demonstrated no survival advantage with completion axillary node dissection (ALND) for patients with T1-2 breast cancer, 1-2 positive sentinel lymph nodes (SLN) who received adjuvant chemoradiation therapy. Over 70% of the cohort had ER+ tumors. There is paucity of data on the adherence rate to Z11, as well as a dearth of data on the applicability of Z11 for the different subtypes. We conducted a large hospital-based study to evaluate the adherence rate to Z0011 based on subtypes.

METHODS: The National Cancer Data Base was queried to evaluate 33,859 patients diagnosed with T1-2, N1, and M0 breast cancer treated with lumpectomy with negative margins, and adjuvant chemoradiation therapy between 2012 and 2018. Patients were classified into 3 groups: (1) ER+/HER2-, (2) ER-/HER2-, (3) HER2+ regardless of ER status. The revised Scope of the Regional Lymph Node Surgery 2012 was used to classify patients into those who underwent a sentinel lymph node biopsy (SLN) or an axillary lymph node dissection (ALND). Differences in utilization of ALND by subtypes were compared. The Kaplan-Meier method and log-rank test were used to compare overall survival (OS). P-value < 0.05 was considered statistically significant.

RESULTS: For ER+/HER2-, ER-/HER2-, and HER2+ tumors, the rate of ALND was 43.6%. 50.2%, and 47.8%, respectively. The 5-year OS for SLN and ALND for the entire cohort was 94.0% and 93.1% (P=0.0004); for ER+/HER2-, it was 95.4% and 94.7% (P=0.04); for ER-/HER2-, it was 84.1% and 84.3% (p=0.41); for HER2+, it was 94.2% and 93.2% (P=0.20). Multivariable Cox Proportional Hazard regression analysis demonstrated no significant survival differences between SLN or ALND (P=0.776).

CONCLUSIONS: Z11 is applicable for women with early N1 disease, regardless of subtypes. ALND did not confer a survival advantage over SLN. Despite this, up to 50% of patients who fit Z11 criteria continue to undergo ALND.