Impact of AJCC prognostic staging on prognosis and postmastectomy radiotherapy decision-making in hormone receptor-positive and HER2-positive breast cancer

AJCC pathological prognostic staging downstaged 74.7 per cent of patients with breast cancer with hormone receptor-positive and HER2-positive disease but does not provide better risk discriminatory ability in predicting prognosis than anatomical staging. However, pathological prognostic staging is valuable in providing prognostic counselling to patients and may also guide postmastectomy radiotherapy decision-making. Background The role of postmastectomy radiotherapy (PMRT) in patients with node-positive hormone receptor-positive (HoR) and HER2-positive breast cancer (BC) regarding AJCC pathological prognostic staging (PPS) has not been fully determined. This study aimed to validate PPS in patients with node-positive HoR+/HER2(+) BC after mastectomy and to investigate the role of PPS on PMRT decision-making in this patient subset. Methods Patients diagnosed with BC from the Surveillance, Epidemiology, and End Results database were included. Patients were classified based on the anatomical staging (AS) and PPS. Breast cancer-specific survival (BCSS) was calculated. Results In total, 6862 patients were included: 4306 (62.8 per cent) patients received PMRT and 2556 (37.2 per cent) patients had not. Compared to AS, PPS downstaged 5260 patients (76.7 per cent) and no patients were upstaged. The C-index was similar between PPS and AS (0.690 versus 0.682; P = 0.346). Regarding AS, patients who received PMRT had significantly better BCSS than those who had not in stage IIIA (P = 0.017) and stage IIIC (P < 0.001) disease, but not in stage IB (P = 0.675), IIA (P = 0.677), IIB (P = 0.100), and IIIB (P = 0.747) disease. Regarding PPS, patients who received PMRT had significantly better BCSS than those who had not in stage IIIA (P = 0.038) and stage IIIB (P = 0.017) disease, but not in stage IA (P = 0.336), IB (P = 0.893), IIA (P = 0.815), and IIB (P = 0.120) disease. PPS might allow approximately 1390 stage III patients (45.0 per cent) in the AS criterion to avoid PMRT. Conclusion PPS does not provide better risk discriminatory ability in predicting prognosis than AS in patients with node-positive HoR+/HER2(+) BC after mastectomy. However, PPS is valuable in providing prognostic counselling to patients and may also guide PMRT decision-making.