PALLAS will assess if adding a drug called palbociclib, when combined with standard endocrine treatment for a subtype of early-stage breast cancer called “luminal,” improves the outcome of patients with the disease. It will also assess the safety profile of this combination and try to identify specific molecular markers to predict which patients will benefit most from this treatment combination.

Palbociclib is a drug that may stop cancer cells from growing.  It blocks the activity of two closely related enzymes (proteins that help chemical reactions occur in the body), called cyclin D kinases 4 and 6 (CDK 4/6). These proteins are part of a pathway, or a sequence of steps, which is known to regulate cell growth. Laboratory testing has suggested that palbociclib may stop the growth of breast cancer cells of the luminal subtype.

Endocrine therapy in this study will consist of either tamoxifen or aromatase inhibitors (anastrozole, letrozole, exemestane), both being well-established endocrine therapy options used for patients with early stage breast cancer.

The standard treatment for the luminal subtype of breast cancer is endocrine therapy: this is a therapy that prevents breast cancer cell growth by blocking oestrogen stimulation. Despite its success, some patients still develop recurrence of their disease. Clinical studies in late stage (metastatic) breast cancer have shown that combining palbociclib with endocrine therapy provides better control. PALLAS will evaluate this approach for patients with early-stage disease.

The main objective of PALLAS is to compare the clinical benefits and the effects of giving 2 years of palbociclib in combination with standard endocrine therapy, versus standard endocrine therapy alone.

Results of the second interim analysis of the PALLAS study were published online in The Lancet Oncology in February 2021.

Despite the unexpected negative results showing that the addition of palbociclib to endocrine therapy had no effect on invasive disease-free survival (iDFS; i.e. reducing the chance of the cancer coming back, or of dying or getting another cancer) compared to standard of care, PALLAS is a great example of worldwide collaboration between academia and industry to run a huge pivotal clinical trial and advance breast cancer research. It will enable us to know more about the effects of palbociclib in the treatment of patients with hormone receptor-positive (HR+) HER2-negative early breast cancer.

Patients enrolled in PALLAS were randomly assigned to two different groups. After the surgical procedure to remove the primary breast tumour, patients received either:
– palbociclib for 2 years in combination with standard endocrine treatment for at least 5 years.
– standard endocrine treatment for at least 5 years.

5,796 patients who have the luminal subtype of early breast cancer (hormone receptor-positive ([HR+]/ human epidermal growth factor receptor 2 [HER2]-negative early breast cancer).

The PALLAS trial is being conducted collaboratively by several academic-based global research groups.

PALLAS is co-sponsored by the Austrian Breast & Colorectal Cancer Study Group (ABCSG) and Alliance Foundation Trials (AFT) as part of a clinical research collaboration with Pfizer (providing study drug and funding) and other study groups, including PrECOG, LLC; NSABP Foundation Inc; and the Breast International Group (BIG).

The study started in 2015 and was stopped prematurely in May 2020 by the study’s Steering Committee following the Independent Data Monitoring Committee’s assessment that adding the drug palbociclib to the current standard treatment would not significantly reduce the chance of the cancer coming back, or of dying or getting another cancer and that this was not going to change over time. However, no specific safety issues related to the drug were reported.

Patients in PALLAS are no longer receiving palbociclib but they are being followed up as planned in order to gather long term data about the use of palbociclib, which has been proven to be effective in metastatic patients and therefore is a drug that is and will continue to be used by those patients. 

Read the press release issued on 29 May 2020 

Results of the second interim analysis of the PALLAS study were published online in The Lancet Oncology in February 2021.

170 hospitals in the U.S. and approximately 235 hospitals in Europe, Canada, Australia, Japan, South Korea, and Israel are participating.

• Pfeiler G, Hlauschek D, Mayer EL, et al. Impact of BMI in Patients With Early Hormone Receptor-Positive Breast Cancer Receiving Endocrine Therapy With or Without Palbociclib in the PALLAS Trial. J Clin Oncol. Published online August 9, 2023:JCO2300126. doi:10.1200/JCO.23.00126

  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). JCO. 2022;40(3):282-293. doi:10.1200/JCO.21.02554
• Mayer EL, Dueck AC, Martin M et al. Palbociclib with adjuvant endocrine therapy in early breast cancer (PALLAS): interim analysis of a multicentre, open-label, randomised, phase 3 study. The Lancet Oncology. Volume 22, Issue 2, February 2021, Pages 212-222.
• Mayer EL, Demichele AM, Pfeiler G et al. PALLAS: PALbociclib CoLlaborative Adjuvant Study: A randomized phase Ill trial of palbociclib with standard adjuvant endocrine therapy versus standard adjuvant endocrine therapy alone for HR+/HER2- early breast cancer. Annals of Oncology (2017) 28 (suppl_5): v43-v67. 10.1093/annonc/mdx362

The study is funded thanks to a grant from Pfizer, and run according to BIG’s Principles of Research Conduct.

NCT02513394