An experimental drug may help treat patients with hormone-resistant breast cancer, scientists say.
Palbociclib, an investigational oral medication that works by blocking molecules responsible for cancer cell growth, is well tolerated and extends progression-free survival (PFS) in newly diagnosed, advanced breast cancer patients, including those whose disease has stopped responding to traditional endocrine treatments, researchers said.
The phase II study of palbociclib was led by researchers in the Abramson Cancer Center and the Perelman School of Medicine at the University of Pennsylvania.
Earlier phase I results by researchers at Penn Medicine contributed to the development of palbociclib, which was recently approved by the US Food and Drug Administration (FDA) for metastatic breast cancer patients just beginning to undergo endocrine therapy.
“The FDA approval has expanded treatments options for many metastatic breast cancer patients, but these new results are showing how effective the drug can also be for breast cancer patients who have already tried endocrine therapies and may be running out of options,” said lead investigator Angela DeMichele, co-leader of the Breast Cancer Research Programme at the Abramson Cancer Center.
“Combined with the promising results from other trials looking at the effectiveness of this drug, our results indicate that palbociclib can extend the duration of disease control and produce tumour shrinkage in patients with estrogen-receptor positive (ER+) breast cancer, without the debilitating side effects of chemotherapy,” DeMichele said.
The newly-published phase II trial primarily sought to evaluate disease response and control, while monitoring for the presence of side effects such as neutropenia, an abnormally low white blood cell count.
Patients enrolled in the trial had previously undergone several prior chemotherapy and hormonal regimens for metastatic disease. Palboclib was administered once daily for 21 days each month.
Researchers noted a median PFS, the time before a tumour worsens or the patient dies, of 3.7 months for patients taking the drug.
However, patients with hormone receptor-positive (HR+) breast cancer - where the breast cancer cells depend on the hormones estrogen and progesterone to grow - had significantly longer PFS (5.1 months) compared to that of the HR-negative group.
Those who had previously progressed through at least two rounds of hormonal therapy saw significantly greater benefits.
“The drug was extremely well-tolerated in this trial, and the absence of symptoms commonly associated with cancer treatment, such as nausea, diarrhea, or pain was remarkable,” said senior author Peter O’Dwyer, a professor in the division of Hematology/Oncology.
The research was published in the journal Clinical Cancer Research.