Utilization and Outcomes of the 21-Gene Recurrence Score in pN2 Breast Cancer Patients

The 21-gene assay recurrence score (RS) can guide the use of chemotherapy for the management of patients with pN0- 1 [1-3 positive lymph nodes (LNs)] breast cancer. However, practice patterns based on this assay, as well as associated outcomes, have not been evaluated for patients with pN2 (4-9 positive LNs) disease.

The National Cancer Database (NCDB) was queried for patients with newly-diagnosed, non-metastatic, hormone receptor-positive, Her2-negative, pN2 breast cancer who underwent adjuvant endocrine therapy and had a known RS. Kaplan-Meier analysis was used to evaluate overall survival (OS); Cox proportional hazards modeling determined variables associated with OS.

Of 1,658 patients, 1,109 (67%) received chemotherapy and 549 (33%) did not. Chemotherapy was administered to 54% of patients with a low-risk recurrence score (RS), 67% with intermediate-risk RS, and 75% with high-risk RS. Chemotherapy was associated with improved 5-year OS in low-risk RS (95.5% vs. 87.4%), intermediate-risk RS (91.9% vs. 83.5%), and high-risk RS (81.3% vs. 50.2%) (p≤0.001 for all). On Cox multivariable analysis, chemotherapy and the RS risk group significantly associated with OS (p<0.05 for both). Qualitatively, patients over 70 years of age appeared to benefit comparatively less from chemotherapy.

Despite the underutilization of chemotherapy for hormone receptor-positive, Her2-negative, pN2 patients, it was associated with improved OS for all 21-gene panel risk groups. These results support the existing standard of chemotherapy for this population, although omission could be considered in patients over 70 years of age.