The following article features coverage from the 2021 San Antonio Breast Cancer Symposium. Click here to read more of Cancer Therapy Advisor’s conference coverage.

The addition of palbociclib to adjuvant endocrine therapy did not improve survival when compared with endocrine therapy alone among patients with early-stage, hormone receptor (HR)-positive and HER2-negative breast cancer, according to the final analysis of the phase 3 PALLAS trial.

The results were presented at the 2021 San Antonio Breast Cancer Symposium (SABCS) and simultaneously published in the Journal of Clinical Oncology.1,2

“Benefits previously observed in the metastatic setting with palbociclib did not translate into the earlier curative adjuvant setting,” said study author Michael Gnant, MD, of the Medical University of Vienna in Austria.

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The open-label, phase 3 PALLAS trial ( Identifier: NCT02513394) included 5761 patients with stage II-III, HR-positive, HER-negative breast cancer. They were randomly assigned to adjuvant treatment with 5 years of endocrine therapy (aromatase inhibitor or tamoxifen with or without a luteinizing hormone-releasing hormone) with or without 2 years of palbociclib.

The primary endpoint was invasive disease-free survival (iDFS), and secondary endpoints included distant recurrence-free survival (DRFS), locoregional recurrence-free survival (LRRFS), overall survival (OS), and safety.

Active treatment with palbociclib was stopped in May 2020 due to futility, and the remaining patients who were receiving palbociclib were transferred to follow-up. This presentation was the final analysis of the trial data, with a median follow-up of 31 months.

Palbociclib added to adjuvant endocrine therapy failed to improve iDFS. The 4-year iDFS rate was 84.2% with palbociclib and 84.5% with endocrine therapy alone (hazard ratio [HR], 0.96; 95% CI, 0.81-1.14; P =.65).

All secondary efficacy outcomes were also similar between the treatment arms.

Palbociclib was discontinued early by 42% of patients, with 28.2% of discontinuations related to adverse events (AEs). However, there was no significant benefit with the addition of palbociclib among patients who completed or nearly completed treatment, suggesting that the negative result of the PALLAS trial was not due to insufficient exposure to the drug, Dr Gnant said.

The most common grade 3-4 AE with palbociclib was neutropenia, which occurred in 61.9% of patients, compared with 0.4% of patients in the endocrine therapy-only arm.

Dr Gnant said he and his colleagues will continue long-term follow-up and work to better understand the biology of luminal breast cancer.

Disclosures: PALLAS is sponsored by Alliance Foundation Trials, LLC. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.

Read more of Cancer Therapy Advisor’s coverage of SABCS 2021 by visiting the conference page.


  1. Gnant M, Dueck AC, Frantal S, et al. Adjuvant palbociclib in HR+/HER2- early breast cancer: Final results from 5,760 patients in the randomized phase III PALLAS trial. Presented at SABCS 2021; December 7-10, 2021; San Antonio, TX. Abstract GS1-07.
  2. Gnant M, Dueck AC, Frantal S, et al. Adjuvant palbociclib for early breast cancer: The PALLAS trial results (ABCSG-42/AFT-05/BIG-14-03). Published online December 7, 2021. doi:10.1200/JCO.21.02554