The following article features coverage from the European Society for Medical Oncology 2020 virtual meeting. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

Treatment of early hormone receptor (HR)-positive, HER2-negative breast cancer with palbociclib for 2 years provided no additional benefit over endocrine therapy alone, according to results of the phase 3 PALLAS trial reported at the European Society of Medical Oncology (ESMO) Virtual Congress 2020.

“The benefits observed in the metastatic setting with palbociclib did not translate into the earlier adjuvant setting,” Erica Mayer, MD, MPH, of the Dana-Farber Cancer Institute in Boston, Massachusetts, and presenter of the study, said.

The international, open-label, phase 3 PALLAS trial randomly assigned 5760 patients with stage II-III HR-positive, HER2-negative breast cancer to receive palbociclib for 2 years plus adjuvant endocrine therapy or endocrine therapy alone. The primary endpoint was invasive disease-free survival (iDFS) and secondary endpoints included recurrence and safety.

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The median patient age at baseline was 52 years, and 33% and 49% of patients had stage IIB or III disease, respectively. Most patients had received prior chemotherapy (83%), and initial adjuvant endocrine therapy was an aromatase inhibitor (67%) or tamoxifen (33%). Approximately 20% of patients were receiving a concurrent adjuvant luteinizing hormone-releasing hormone agonist.

Futility was reached at the second interim analysis and the independent monitoring committee recommended discontinuation of palbociclib.

There was no significant difference in iDFS between arms after a median follow-up of 23.7 months, with a rate of 88.2% in the palbociclib plus endocrine therapy arm compared with 88.5% in the endocrine therapy only arm (hazard ratio, 0.93; 95% CI, 0.76-1.15; P =.51), which was consistent across subgroups.

There was also no difference between arms in distant recurrence–free survival.

Adverse events (AEs) were more common in the palbociclib arm, including grade 3 to 4 neutropenia and leukopenia. Early discontinuation of palbociclib occurred among 42.2% of patients, with the majority (64.2%) due to unacceptable toxicity. Dose reductions of palbociclib were also common, with approximately 60% of patients requiring a reduction by 6 months and approximately 90% by 24 months.

The results of this interim analysis demonstrated that “the addition of palbociclib to adjuvant endocrine therapy did not prolong iDFS compared to endocrine therapy alone in patients with stage II-III H-positive/HER2-negative breast cancer,” Dr Mayer concluded.

Disclosures: The study was funded by Pfizer, Inc.. Some of the presenters reported financial relationships with the pharmaceutical industry. For a full list of disclosures, please refer to the original abstract.

Read more of Cancer Therapy Advisor‘s coverage of the ESMO Virtual Congress 2020 by visiting the conference page.


Mayer EL, Gnant MI, DeMichele A, et al. PALLAS: A randomized phase III trial of adjuvant palbociclib with endocrine therapy versus endocrine therapy alone for HR+/HER2- early breast cancer. Presented at: European Society of Medical Oncology (ESMO) Virtual Congress 2020; September 19-21, 2020. LBA12.