Efficacy and safety of neoadjuvant stereotactic body radiation therapy plus dalpiciclib and exemestane for hormone receptor-positive, HER2-negative breast cancer: A prospective pilot study

  1. Yu Zhang
  2. Shuo Cao
  3. Nan Niu
  4. Huilian Shan
  5. Jinqi Xue
  6. Guanglei Chen
  7. Yongqing Xu
  8. Jianqiao Yin
  9. Chao Liu
  10. Lisha Sun
  11. Xiaofan Jiang
  12. Meiyue Tang
  13. Qianshi Xu
  14. Mingxuan Jia
  15. Xu Zhang
  16. Zhenyong Zhang
  17. Qingfu Zhang
  18. Jianfei Wang
  19. Ailin Li
  20. Yongliang Yang
  21. Caigang Liu
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Abstract

Background

Both neoadjuvant chemotherapy and endocrine therapy only result in trivial pathological complete response rates and moderate objective response rates (ORR) in hormone receptor (HR)-positive, human epidermal growth factor receptor-2 (HER2)-negative breast cancer, more promising alternatives are urgently needed. With proven synergistic effect of cyclin dependent kinase 4/6 (CDK4/6) inhibitor and radiotherapy in preclinical studies, this pilot study aimed to explore the efficacy and safety of neoadjuvant stereotactic body radiation therapy (SBRT) followed by dalpiciclib and exemestane in HR-positive, HER2-negative breast cancer.

Methods

This was a single-arm, non-controlled prospective pilot study. Treatment-naïve patients with unilateral HR-positive, HER2-negative breast cancer received neoadjuvant radiotherapy (24Gy/3F) followed by dalpiciclib and exemestane for 6 cycles. The primary endpoint was the proportion of patients with residual cancer burden (RCB) score of 0-I. Key secondary endpoints included ORR, breast-conservation rate, biomarker analysis, and safety.

Results

All 12 enrolled patients completed the study treatment and surgery. Two (16.7%) of them achieved the RCB 0-I with the ORR of 91.7% (11/12). Analyses of tumor specimens showed significant increase of infiltrating T cells rather than alteration of PD-L1 positive immune cells. The most common grade 3 adverse events (AEs) were neutropenia (66.7%) and leukopenia (25.0%), but no grade 4-5 AE or death occurred.

Conclusions

Our results suggested neoadjuvant SBRT followed by dalpiciclib and exemestane are effective and tolerable, and provides novel insights for the neoadjuvant treatment of HR+/HER2-breast cancer, which may be considered as a feasible option for patients with HR-positive, HER2-negative breast cancer.

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