Impact of 21-Gene Expression Assay on Staging Estrogen Receptor–Positive HER2-Negative Breast Cancer

Abstract Purpose The 8th edition of the American Joint Committee on Cancer (AJCC) breast cancer staging system requires histologic grade (GR), estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and stage (assessed by the tumor, node, metastasis classification system). For T1-2 N0, ER + /HER2− tumors, if the 21-gene expression assay is ordered and Oncotype DX (ODX) recurrence score (RS) is 0 to 10, the stage is IA. The purpose of this study was to determine the impact of the ODXRS on staging ER + /HER2− tumors. Materials and Methods This is a retrospective review of ER + /HER2− invasive breast cancer (BC) with ODXRS results from 2 institutions (n = 816) between 2006 and 2018. Stage based on the AJCC 7th and 8th editions, and stage using the 8th edition with and without ODXRS were compared. Significant associations among pathologic parameters and ODX risk groups were determined. Clinical histories were reviewed. Results Nearly half of the patients (43%) had a change in BC stage using the new staging system. Only 4 patients changed stage as a direct result of ODXRS. Influence of ODXRS on staging is limited to T2N0 tumors that are either GR 3 and strongly ER + and PR + or GR 1-2 and ER + /PR−. Sixty-one percent of cases of recurrence (11/18) were downstaged using the new staging system. Conclusion ODXRS has little influence on staging, thus supporting the view of the AJCC 8th edition expert panel that ODX is not required for staging. Downstaging of more than half of cases of recurrence suggests that continued refinement of the staging system, as proposed by the expert panel, could be beneficial in this subgroup of patients.