ABSTRACT
BACKGROUND: The American Joint Commission Cancer (AJCC) Cancer Staging Manual 8th edition introduced a breast cancer (BC) Prognostic Stage (PS) that combines tumour grade, oestrogen (ER), progesterone (PgR), and human epidermal growth factor-2 (HER2) receptor status with Anatomic TNM Stage (AS). In a further modification, patients with early BC and an Oncotype DX® Recurrence Score (RS) < 11 are assigned to PS 1A irrespective of grade and size up to 5 cm. This study profiles the impact of these changes on staging in patients with early BC and RS < 11. METHODS: A total of 127 patients, with primary BC and RS < 11, were identified from a consecutive series of 729 patients with ER-positive, HER2-negative, lymph node-negative, primary BC whose tumours were tested using the Oncotype DX® 21 multigene assay. Each patient was assigned AS, PS, and RS-modified PS, and staging categories were compared. RESULTS: Applying AS, 100 patients were stage IA and 27 IIA. Applying PS, 89 were stage IA, 33 IB, 4 IIA, and 1 IIB. All patients were IA according to RS-modified PS. Comparing PS to AS, 26.7% of patients (n = 34) changed stage, 9.4% (n = 12) to a higher and 17.3% (n = 22) to a lower stage. RS-modified PS versus AS resulted in downstaging in 21.3% (n = 27). Comparing PS modified by RS to PS alone, 29.9% (n = 38) were downstaged. CONCLUSION: Application of PS and RS-modified PS results in tumour downstaging in approximately 20% of patients with early BC. Upstaging was observed in 9% of patients when staged according to PS and was primarily due to the impact of high histological grade.