The combination of Ibrance® (palbociclib) and Faslodex® (fulvestrant) appears to extend progression-free survival in women with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER)-negative metastatic breast cancer. These findings were presented at 2015 Annual Meeting of the American Society of Clinical Oncology (May 29–June 2, Chicago, Illinois) and published in the New England Journal of Medicine.

The majority of breast cancers are hormone receptor-positive. These cancers are stimulated to grow by the circulating female hormones estrogen and/or progesterone. Treatment of hormone receptor-positive breast cancer often involves hormonal therapies that suppress or block the action of estrogen.

Ibrance is approved for use in combination with Femara® (letrozole) for the treatment of postmenopausal women with ER-positive, HER2-negative advanced breast cancer. As part of 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 ER-positive breast cancer. In this recent Phase III study, known as the PALOMA3 trial, Ibrance was tested in combination with Faslodex for the treatment of patients with advanced hormone-receptor-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 ER-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.

Ibrance appeared to more than double progression-free survival. Women who received the kinase inhibitor plus Faslodex had a median progression-free survival of 9.2 months, compared with 3.8 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.

It appears that the combination of Ibrance plus Faslodex can extend progression-free survival in patients with metastatic ER-positive, HER2-negative breast cancer whose disease has progressed after previous hormonal therapy. This is a promising outcome for patients for whom hormonal therapy has not been successful.

Reference: 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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