Results from the stage three breast cancer clinical trial, PALLAS, has provided insight for future trials into early stage breast cancer.

The PALLAS Clinical Trial

The PALLAS clinical trial has provided a wealth of material for future research into early-stage breast cancer.

The PALLAS trial studied the effects of adding a two-year course of palbociclib, a cell cycle inhibitor, to standard hormone-blocking treatment for patients with hormone-receptor-positive, HER2-negative early breast cancer.

PALLAS was an international clinical trial that recruited 5,795 patients worldwide, including more than 430 patients from Australia.

Researchers had hoped that palbociclib, currently used in patients with metastatic breast cancer to prolong the duration of cancer control and delay the need for chemotherapy, might reduce the risk of metastatic recurrence in patients with earlier stages of breast cancer.

“We were aiming to find patients who stood to gain the most from the study drug, based on their higher risk of recurrence,” says Dr Nicholas Zdenkowski, the Breast Cancer Trials Study Chair of the PALLAS clinical trial.

“All patients received standard hormone-blocking treatment and half received the additional palbociclib.

They had also received chemotherapy and radiotherapy if their treating doctor considered those treatments appropriate.”

However, interim results showed palbociclib wasn’t working in this setting, he says. “Over time, it was seen there was no difference between the groups, so the study drug was stopped in those who were still taking it as part of their planned two-year course.”

He’s not disheartened, though. “You read the headline, and you think it’s disappointing,” says Dr Zdenkowski. “But these large trials are always designed so we learn things, and we’ll continue to learn as we follow these patients up. We know recurrences can occur years down the track, and a difference may emerge over time between the two study groups.”

During the trial, researchers gathered a bio-bank of tissue samples from patients’ surgeries for analysis, along with blood samples over the course of their participation.

“That will provide some powerful information about the potential for some patients to benefit from palbociclib, about possible resistance mechanisms, and a range of other useful data,” says Dr Zdenkowski.

Data from ongoing patient questionnaires is also expected to provide insights into the patients’ perspectives on endocrine therapy and palbociclib, as well as their experience with breast cancer.

So, although this particular use of palbociclib has not been proven effective, its current use in patients with metastatic breast cancer will continue, and so will the research, says Dr Zdenkowski. “We’re not able to rest until all people have been cured of their cancer.” [ends]


Palbociclib with adjuvant endocrine therapy in early breast cancer (PALLAS): interim analysis of a multicentre, open-label, randomised, phase 3 study.

Mayer EL, Dueck AC, Martin M, Rubovsky G, Burstein HJ, Bellet-Ezquerra M, Miller KD, Zdenkowski N, Winer EP, PFeiler G, Goetz M, Ruiz-Borrego M, Anderson D, Nowecki Z, Loibl S, Moulder S, Ring A, Fitzal F, Traina T, Chan A, Rugo HS, Lemieux J, Henao F, Lyss A, Antolin Novoa S, Wolff AC, Vetter M, Egle D, Morris PG, Mamounas EP, Gil-Gil MJ, Prat A, Fohler H, Metzger Filho O, Schwarz M, DuFrane C, Fumagalli D, Puyana Theall K, Ray Lu D, Huang Bartlett C, Koehler M, Fesl C, DeMichele A, Gnant M. Lancet Oncology. 2021; epub 15 January 2021; https://doi.org/10.1016/S1470-2045(20)30642-2.


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Dr Nicholas Zdenkowski

Dr Nicholas Zdenkowski is the Medical Advisor at Breast Cancer Trials, a BCT researcher and medical oncologist.

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