Neoadjuvant systemic therapy in breast cancer: use and trends in radiotherapy practice.

Background The use of neoadjuvant systemic therapy (NAST) in the treatment of breast cancer is increasing, and the role of adjuvant radiation therapy (RT) in that setting is uncertain. We sought to review and report the use of NAST, its trends over time, and its relationship with the prescribing patterns of locoregional RT in a provincial cancer system. Methods Patients with stages I-III breast cancer diagnosed during 2007-2012 were identified using a provincial database. Patient, tumour, and treatment characteristics were extracted. Multivariable logistic regression analyses were used to assess associations with the use of NAST. Kaplan-Meier and Cox regression were used for survival analyses. Results Of the 11,658 patients who met the inclusion criteria, 602 (5%) had received NAST. Use of NAST was more frequent in stage III patients (53%) than in stages I and II patients (2%). In clinically lymph-node positive patients, a pathology assessment was made approximately 50% of the time. Higher clinical tumour stage and increasing clinical nodal stage predicted for increasing use of NAST and of nodal RT after NAST, but pathologic nodal status after NAST was not associated with use of nodal RT. A statistically significant survival difference was observed between patients in the NAST and no-NAST groups, but that significance disappeared in a multivariable Cox regression analysis. Conclusions This population-based study demonstrated 5% use of NAST for breast cancer. Most patients received nodal RT after NAST, and nodal RT was not associated with pathologic stage after NAST. Findings likely reflect the realities of clinical practice and show that reliance on clinical nodal staging results in outcomes similar to those reported in the literature.