Oncology · Medical Literature
A phase II clinical trial of neoadjuvant chemotherapy combined with immunotherapy and different radiotherapy fractionation regimens in HR+/HER2- breast cancer.
Abstract
The modest neoadjuvant response in early-stage HR+/HER2- breast cancer necessitates novel treatment intensification strategies. While radiotherapy can enhance systemic efficacy via immune modulation, the optimal fractionation for integration with immunochemotherapy remains unknown. This multicenter phase II study aims to evaluate the feasibility, safety, and preliminary efficacy of Toripalimab combined with chemotherapy and tumor-directed radiotherapy, specifically investigating three distinct fractionation schedules. This prospective, multicenter, three-cohort exploratory study enrolls treatment-naïve patients with early-stage HR+/HER2- breast cancer. Participants receive neoadjuvant Toripalimab plus chemotherapy alongside image-guided radiotherapy restricted to the primary tumor. Cohorts are differentiated by fractionation regimen: Arm 1 (8 Gy × 3 fractions, total 24 Gy); Arm 2 (16 Gy single fraction); Arm 3 (0.5 Gy twice daily for 8 cycles, cumulative 8 Gy). A total of 45 patients (15 per cohort) will be enrolled. The primary endpoint is pathological complete response (pCR). Secondary endpoints include objective response rate, recurrence, survival outcomes (OS, EFS, DMFS, IDFS, IBTR), and safety. This exploratory study will provide feasibility, tolerability, and preliminary efficacy data for a novel multimodal neoadjuvant strategy combining different radiotherapy fractionation patterns with immunotherapy and chemotherapy. Given the descriptive analytical framework, findings are expected to be hypothesis generating and will inform the selection of radiotherapy schedules for future larger-scale randomized trials aimed at improving outcomes in HR+/HER2- breast cancer. http://www.chictr.org.cn, identifier NCT06639672.
Clinical relevance
HR+/HER2- breast cancer represents the largest molecular subtype of breast cancer yet historically achieves the lowest pathological complete response (pCR) rates with standard neoadjuvant chemotherapy, underscoring a critical unmet need for treatment intensification. This phase II trial addresses the biologically rational but clinically underexplored strategy of integrating tumor-directed radiotherapy—leveraging its immunostimulatory abscopal and in-situ vaccination effects—with PD-1 checkpoint inhibition (Toripalimab) and chemotherapy in the neoadjuvant setting. Clinicians should take note as this represents one of the first prospective, multicenter efforts to systematically compare distinct radiotherapy fractionation schedules within a trimodal neoadjuvant backbone specifically for this immunologically 'cold' subtype.
Key findings
1. Study design: Prospective, multicenter, three-cohort exploratory phase II trial enrolling 45 treatment-naïve patients with early-stage HR+/HER2- breast cancer (15 patients per cohort); pCR is the primary endpoint. 2. Arm 1 fractionation: Hypofractionated radiotherapy at 8 Gy × 3 fractions (total 24 Gy) delivered to the primary tumor concurrent with Toripalimab plus chemotherapy. 3. Arm 2 fractionation: Single-fraction stereotactic/ablative radiotherapy at 16 Gy to the primary tumor, hypothesized to maximize immunogenic cell death via high-dose-per-fraction delivery. 4. Arm 3 fractionation: Ultra-low-dose radiotherapy (ULDR) at 0.5 Gy twice daily for 8 cycles (cumulative 8 Gy), targeting immunosuppressive tumor microenvironment remodeling rather than direct cytotoxicity. 5. Secondary endpoints include objective response rate (ORR), overall survival (OS), event-free survival (EFS), distant metastasis-free survival (DMFS), invasive disease-free survival (IDFS), ipsilateral breast tumor recurrence (IBTR), and comprehensive safety profiling. 6. NOTE: As this is a registered trial protocol publication (not a results paper), no efficacy or toxicity outcome data, effect sizes, confidence intervals, p-values, or NNT/NNH are yet available; all quantitative findings are limited to design parameters as reported in the abstract.
Practice implications
At present, this trial should not change clinical practice, as it is a hypothesis-generating protocol study without reported outcome data; clinicians should await peer-reviewed efficacy and safety results before adopting any of these fractionation strategies outside of a trial setting. Patient selection for future enrollment or analogous institutional protocols should focus on treatment-naïve, early-stage HR+/HER2- breast cancer patients where standard neoadjuvant chemotherapy pCR rates are insufficient, and where there is no contraindication to PD-1 inhibition or tumor-directed radiotherapy. The three-arm design will be particularly valuable in informing whether ablative (16 Gy single fraction), moderate hypofractionation (24 Gy in 3 fractions), or ultra-low-dose immunomodulatory radiotherapy (8 Gy total) is the optimal fractionation partner for immunochemotherapy, directly guiding the radiotherapy schedule selection for subsequent powered randomized controlled trials.