Cancer Res Treat.  2021 Jul;53(3):695-702. 10.4143/crt.2020.1246.

Implications of Tamoxifen Resistance in Palbociclib Efficacy for Patients with Hormone Receptor-Positive, HER2-Negative Metastatic Breast Cancer: Subgroup Analyses of KCSG-BR15-10 (YoungPEARL)

  • 1Division of Hematology-Oncology, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
  • 2Department of Internal Medicine, Seoul National University Hospital, Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea
  • 3Division of Medical Oncology, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea
  • 4Department of Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
  • 5Department of Hematology-Oncology, Ajou University School of Medicine, Suwon, Korea
  • 6Center for Breast Cancer, National Cancer Center, Goyang, Korea
  • 7Department of Internal Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea
  • 8Division of Medical Oncology, Department of Internal Medicine, Gachon University Gil Medical Center, Incheon, Korea


YoungPEARL (KCSG-BR15-10) trial demonstrated a significant progression-free survival (PFS) benefit for premenopausal patients with hormone receptor–positive/human epidermal growth factor receptor 2–negative (HR+/HER2–) metastatic breast cancer (MBC) for palbociclib plus exemestane with ovarian function suppression compared to capecitabine. However, the number of tamoxifen-sensitive premenopausal patients was small because most recurrences occurred early during adjuvant endocrine therapy (ET), with tamoxifen being the only drug used; hence, the data for these patients were limited. Here we present a subgroup analysis according to tamoxifen sensitivity from the YoungPEARL study. Materials and Methods Patients were randomized 1:1 to receive palbociclib+ET (oral exemestane 25 mg/day for 28 days, palbociclib 125 mg/day for 21 days, plus leuprolide 3.75 mg subcutaneously every 4 weeks) or chemotherapy (oral capecitabine 1,250 mg/m2 twice daily for 14 days every 3 weeks). Tamoxifen resistance was defined as: relapse while on adjuvant tamoxifen, relapse within 12 months of completing adjuvant tamoxifen, or progression while on first-line tamoxifen within 6 months for MBC.
In total, 184 patients were randomized and 178 were included in the modified intention-to-treat population. PFS improvement in the palbociclib+ET group was observed in tamoxifen-sensitive patients (hazard ratio, 0.38; 95% confidence interval, 0.12 to 1.19). Furthermore, palbociclib+ET prolonged median PFS compared with capecitabine in tamoxifen-sensitive (20.5 months vs. 12.6 months) and tamoxifen-resistant (20.1 months vs. 14.5 months) patients. Palbociclib+ET demonstrated a higher rate of objective response, disease control, and clinical benefit in tamoxifen-sensitive patients. Conclusion This post hoc exploratory analysis suggests that palbociclib+ET is a promising therapeutic option for premenopausal HR+/HER2– MBC patients irrespective of tamoxifen sensitivity.


Breast neoplasms; Tamoxifen; CDK4/6 inhibitor; Palbociclib; Endocrine therapy
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