Preoperative Radiation Enhances Immune Response in HR-Positive Breast Cancer When Combined with Pembrolizumab
核心洞察
A phase II clinical trial demonstrated that preoperative radiation therapy combined with pembrolizumab significantly improved T-cell (搜索) infiltration in HR-positive, HER2-negative breast cancer (搜索) patients.
The study found dose-dependent improvements in immune response, with 24 Gy radiation showing statistically significant enhancement of T-cell (搜索) infiltration compared to no radiation.
Results suggest radiation therapy could serve as an immune system primer to enhance immunotherapy effectiveness in the most common form of breast cancer (搜索).
A novel approach combining preoperative radiation therapy with immunotherapy has shown promising results in enhancing immune response against hormone receptor (HR)-positive, HER2-negative breast cancer (搜索), according to results from the phase II P-RAD clinical trial presented at the San Antonio Breast Cancer Symposium.
The study, led by Dr. Gaorav Gupta from the University of North Carolina Lineberger Comprehensive Cancer Center (搜索), demonstrated that radiation therapy can significantly improve T-cell (搜索) infiltration (TCI) when administered with pembrolizumab (Keytruda) and chemotherapy before surgery.
Addressing Critical Treatment Gaps
"Many patients with HR-positive, HER2-negative breast cancer (搜索)—the most common type of breast cancer (搜索)—experience late recurrences, and there is a critical need to improve outcomes for this patient population," said Gupta, associate professor of radiation oncology and coleader of the Breast Cancer Research Program. "Immunotherapy has shown early signs of promise, but new strategies are needed to make it more effective in this form of breast cancer."
The research builds on previous findings showing that immune checkpoint inhibitors depend on TCI to effectively counter cancer, and that radiation can mediate improvements in TCI.
Study Design and Patient Population
The Translational Breast Cancer Research Consortium (搜索) enrolled 51 patients with HR-positive, HER2-negative breast cancer (搜索) that had spread to regional lymph nodes. The median patient age was 49.5, with an age range of 23 to 78 years.
Patients were randomly assigned 1:1:1 to receive either no radiation, low-dose radiation (9 Gy), or high-dose radiation (24 Gy) together with pembrolizumab prior to initiating chemotherapy. Radiation doses were administered over three days.
All participants subsequently received 12 weeks of pembrolizumab and paclitaxel, followed by four cycles of pembrolizumab with doxorubicin and cyclophosphamide.
Dose-Dependent Immune Enhancement
The study assessed two coprimary endpoints: TCI at biopsy two weeks after radiation and pathologic complete response in lymph nodes (ypN0) at definitive surgery. Secondary endpoints included pathologic complete response (pCR) and residual cancer burden.
Among 49 patients evaluable for TCI, the proportion of tumors with the highest quartile of TCI increased in a dose-dependent manner: 31% in the 0 Gy arm, 40% in the 9 Gy arm, and 53% in the 24 Gy arm.
While median TCI increased for all patients after treatment, only those in the 24 Gy arm experienced statistically significant improvement in TCI compared to untreated tumors.
Lymph Node Response and Surgical Outcomes
The researchers observed dose-dependent responses in lymph nodes across all 48 evaluable patients. The rate of tumor clearance from surgically removed lymph nodes was 29% overall, showing an increasing trend with radiation dose: 24% at 0 Gy, 29% at 9 Gy, and 33% at 24 Gy.
Secondary endpoints also improved with increasing radiation doses. Overall pCR and residual cancer burden rates were 18% and 27%, respectively. By treatment arm, pCR rates were 6% at 0 Gy, 29% at 9 Gy, and 19% at 24 Gy, while residual cancer burden rates were 18%, 29%, and 33%, respectively. Due to the limited patient numbers, these differences in surgical response rates did not achieve statistical significance.
Clinical Implications and Future Directions
"Modern radiation therapy is safe, precise, and widely available for breast cancer (搜索) treatment," Gupta noted. "Our study suggests that radiation could be used in a new way—to 'prime' the immune system and enhance the effects of immunotherapy in HR-positive, HER2-negative breast cancer (搜索)."
The research provides early evidence that a focused radiation dose of 24 Gy administered over three days, when combined with pembrolizumab, can boost immune activity and may improve tumor clearance before surgery.
Study Limitations and Funding
The study's primary limitation was the limited number of enrolled participants, which affected the statistical power to detect differences in surgical response rates.
The research was supported by Merck (搜索), the Breast Cancer (搜索) Research Foundation, the Translational Breast Cancer Research Consortium (搜索), the Susan G. Komen Foundation, and the Department of Defense Breast Cancer Research Program. Gupta disclosed research funding from Merck and Breakpoint Therapeutics (搜索), royalty payments from Naveris, Inc. (搜索), and an ownership stake in Naveris, Inc.