Lymph Node Status in Breast Cancer Does Not Predict Tumor Biology

The 21-gene Oncotype DXA (R) Breast Recurrence Score(A (R)) (RS) assay has been prospectively validated as prognostic and predictive in node-negative, estrogen receptor-positive (ER+)/HER2- breast cancer patients. Less is known about its prognostic role in node-positive breast cancer. We compared RS results among patients with lymph node-negative (N0), micrometastatic (N1mi), and macrometastatic (N+) breast cancer to determine if nodal metastases are associated with more aggressive biology, as determined by RS. Overall, 610,350 tumor specimens examined by the Genomic Health laboratory from February 2004 to August 2017 were studied. Histology was classified centrally, while lymph node status was determined locally. RS distribution (low: < 18; intermediate: 18-30; high: >= 31) was compared by nodal status. Eighty percent (n = 486,013) of patients were N0, 4% (n = 24,325) were N1mi, 9% (n = 56,100) were N+, and 7% (n = 43,912) had unknown nodal status. Mean RS result was 18, 16.7, 17.3 and 18.9 in the N0, N1mi, N+, and unknown groups, respectively. An RS >= 31 was seen in 10% of N0 patients, 7% of N1mi patients, and 8.0% of N+ patients. The likelihood of an RS >= 31 in N1mi and N+ patients varied with tumor histology, with only 2% of patients with classic infiltrating lobular cancer having an RS >= 31, versus 7-9% of those with ductal carcinoma. RS distribution among N0, N1mi, and N+ patients is similar, suggesting a spectrum of biology and potential chemotherapy benefit exists among node-negative and node-positive ER+/HER2- breast cancer patients. If RxPONDER does not show a chemotherapy benefit in N+ patients with a low RS result, our findings indicate that substantial numbers of patients could be spared the burden of chemotherapy.