V15: Prevalence of pn2/n3 Disease in Postmenopausal Women with cn0 ER+/HER2- breast Cancer

The RxPONDER trial demonstrated that the 21-gene recurrence score can be used to guide adjuvant systemic therapy decisions in postmenopausal women with pN1 ER+/HER2- breast cancer. As such, a sentinel lymph node biopsy (SLNB) may not provide treatment-altering information for many patients. Omission of SLNB in patients with low probability of pN2/N3 disease could be considered. To identify these patients, we characterized the prevalence of pN2/N3 disease and predictors associated with pN2/N3 disease.


Methods:

Women ≥50 years with cN0 ER+/HER2– breast cancer diagnosed between 2013-2016 in the National Cancer Database who underwent breast and axillary surgery without neoadjuvant systemic therapy were included.  Pathologic nodal status was recorded as a dichotomous outcome of pN0/N1 vs pN2/N3. To assess demographic and clinical factors associated with the outcome of nodal status, multivariable logistic regression models were fitted to estimate odds ratios (OR) and 95% confidence intervals (CIs).  


Results:

We included 325,692 women, of whom 81.7% had T1 tumors, 16.8% T2, 1.3% T3, and 0.2% T4. In total, 7,106 (2.2%) were pN2/N3. After adjustment, cT was the strongest predictor of pN2/N3 disease with odds increasing from cT2 (vs. cT1: adjusted risk ratio [aOR] 4.18, 95% CI 3.95-4.42) to cT4 (vs. cT1: aOR 14.93, 95% CI 12.08-18.44). Lobular histology (vs. ductal: aOR 2.41, 95% CI 2.28-2.55), higher grade (G3/G4 vs. G1: aOR 2.88, 95% CI 2.64-3.14), young age (50-59 vs 80+: aOR 1.39, 95% CI 1.25-1.62), and higher Charlson-Deyo score (3 vs 1: aOR 1.37, 95% CI 1.14-1.65) were also associated with increased odds of pN2/N3.  We created a model to estimate prevalence of pN2/N3 using the 3 most predictive factors, Figure 1. Patients with T1 tumors, regardless of tumor grade or histology, had low prevalence of pN2/N3 disease (≤4.2%), and patients with T3/T4 tumors had high prevalence.


Conclusions:

The prevalence of pN2/N3 in postmenopausal women with cN0 ER+/HER2- breast cancer is low, suggesting that omission of SLNB may be reasonable in some otherwise Z0011/AMAROS eligible postmenopausal women. Prospective study is needed to determine safety, including risk of nodal recurrence, of omission of SLNB in low-risk patients.