The United States Food and Drug Administration (FDA) has approved Ibrance (palbociclib) to be used with Faslodex (fulvestrant) for women with hormone-positive (HR-positive), human epidermal growth factor receptor-2 (HER2)-negative, metastatic breast cancer that has progressed following prior endocrine (hormone) therapy.
The majority of breast cancers are HR-positive. These cancers are stimulated to grow by the circulating female hormones estrogen and/or progesterone. Treatment of HR-positive breast cancer often involves hormonal therapies that suppress or block the action of estrogen.
Ibrance belongs to a class of drugs known as kinase inhibitors. Ibrance works by blocking the action of enzymes called kinases. Kinases are involved in many cell functions, including cell signaling, growth, and division. These enzymes may be too active or found at high levels in some types of cancer cells, and blocking them may help keep cancer cells from growing.
Specifically, Ibrance inhibits cyclin-dependent kinase (CDK) 4 and 6. These kinases are involved in the growth of HR-positive breast cancer.
In the recent Phase III trial that prompted the new FDA approval for Ibrance, known as the PALOMA3 trial, Ibrance was tested in combination with Faslodex for the treatment of patients with advanced HR-positive breast cancer. Faslodex is a type of hormonal therapy known as an estrogen receptor antagonist, which blocks the actions of estrogen.
Researchers with the PALOMA3 study enrolled 521 patients with metastatic HR-positive, HER2-negative breast cancer. In all of the patients, cancer had come back or progressed after previous hormonal therapy.
The researchers divided the patients into two groups: one group received Ibrance and Faslodex, and the other group received placebo and Faslodex. Women who were near menopause (pre- and perimenopausal) also received a drug called Zoladex® (goserelin). Zoladex is approved for the treatment of advanced breast cancer in pre- and perimenopausal women to reduce the production of estrogen.
Women who received the kinase inhibitor plus Faslodex had a median progression-free survival of 9.5 months, compared with 4.6 months for those who received placebo plus Faslodex.
Few patients—less than 3%—had to stop treatment with Ibrance due to side effects. Common side effects included neutropenia (low number of immune cells called neutrophils), leukopenia (low number of white blood cells), anemia (low number of red blood cells), thrombocytopenia (low number of platelets), and fatigue.
This new approval provides an additional treatment option for patients with HR-positive, HER2-negative breast cancer that has progressed following prior hormonal therapy.
Turner NC, Ro J, André F, et al. Palbociclib in Hormone-Receptor–Positive Advanced Breast Cancer. New England Journal of Medicine. June 1, 2015DOI: 10.1056/NEJMoa1505270.
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