A pilot phase 2 clinical trial led by researchers at Dana-Farber Cancer Institute is testing the feasibility of the targeted drug palbociclib combined with endocrine therapy as adjuvant therapy for stage II and III breast cancer.
It is one of the only trials in the United States to evaluate palbociclib — a CDK4/6 inhibitor which has shown promising results in metastatic breast cancer — in patients with earlier-stage breast cancer.
A Trials in Progress abstract detailing the study is being presented at the American Society of Clinical Oncology meeting in Chicago on Monday, June 2, 2014, by principal investigator Erica Mayer, MD, MPH, of the Susan F. Smith Center for Women’s Cancers at Dana-Farber. Other sites for the trial are Beth Israel Deaconess Medical Center and Massachusetts General Hospital in Boston, Memorial Sloan Kettering Cancer Center in New York, and University of Pennsylvania Abramson Cancer Center in Philadelphia.
Palbociclib works by blocking cancer cells’ entry into the growth phase of the cell cycle, forcing them to remain in a resting state. Cancer scientists have been cautiously optimistic about the drug’s potential as breast cancer therapy in the wake of favorable clinical trial results reported earlier this year. In that phase 2 trial involving women with hormone-sensitive metastatic breast cancer, the combination of palbociclib with the endocrine agent letrozole almost doubled progression-free survival compared with letrozole alone. A confirmatory phase 3 trial of the combination is ongoing.
Given those encouraging results, Mayer’s study is evaluating the combination of palbociclib with endocrine therapy as adjuvant treatment in non-metastatic breast cancer.
The trial is designed to enroll 160 patients previously treated for stage II or III breast cancer who have already demonstrated tolerance of adjuvant endocrine therapy. Palbociclib will be added to the regimen, and the patients will be monitored for two years. If 50 percent or more of patients discontinue combination treatment, it will be judged as infeasible. A discontinuation rate of 33 percent or less will support the two-year regimen as feasible and allow the combination to move forward in adjuvant development.
“Palbociclib was reasonably well tolerated in the metastatic setting,” said Mayer. “We need to study whether patients who have completed the rigors of adjuvant treatment can also tolerate the addition of this drug to their endocrine therapy.”
The trial is sponsored by Pfizer.
For more information about Dana-Farber research being presented at ASCO, visit www.dana-farber.org/asco.