Palbociclib Receives Breakthrough Designation for Treatment of Breast Cancer

Mace Rothenberg, MD

For the second time in a week, a drug in development has received a “breakthrough therapy designation” from the FDA. This time, the drug palbociclib (formerly known as PD-0332991) has received the designation for the treatment of patients with breast cancer.

Palbociclib is a novel oral selective inhibitor of cyclin-dependent kinase (CDK) 4/6 that prevents cellular DNA synthesis by blocking tumor cell progression. Preclinical studies had previously shown that the compound has significant activity in breast cancer models and acts synergistically with hormonal therapy.

The FDA can assign the breakthrough designation, which was initiated earlier this year, to drugs that treat a life-threatening condition and demonstrate a substantial improvement over existing therapies. The designation promotes an expedited review process by allowing for more meetings between the FDA and the manufacturer during the development process, requiring fewer patients for clinical trials, and reducing the amount of time required for these trials. Pfizer, palbociclib’s manufacturer, can still seek fast-track designation, accelerated approval, and priority review for the drug.

“We appreciate the opportunity that Breakthrough Therapy designation provides to work closely with the FDA on the development of palbociclib,” said Mace Rothenberg, MD, senior vice president of clinical development and medical affairs for Pfizer’s Oncology business unit, in a statement. “Palbociclib is one example of Pfizer’s commitment to identifying and translating innovative science into meaningful new treatment options for cancer patients.”

The results of a two-part phase II study on palbociclib were presented at the 2012 CTRC-AACR San Antonio Breast Cancer Symposium. Postmenopausal women with ER-positive/HER2-negative advanced breast cancer were randomized 1:1 to receive letrozole plus palbociclib or letrozole alone. Pooled results from both parts found that the median PFS was 26.1 months with the combination (95% CI, 12.7—26.1) compared with 7.5 months with letrozole alone (95% CI, 5.6–12.6), a 63% improvement in risk of progression (hazard ratio [HR]=0.37; 95% CI, 0.21–0.63, P < .001).

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Response rates in patients with measurable disease were 45% for the combination arm compared with 31% for letrozole alone. The clinical benefit rate, which represented complete and partial response rates plus stable disease, was 70% versus 44%, respectively.

A randomized, multicenter, double-blind phase III study called Study 1008 has been initiated. In that study, palbociclib and letrozole will be compared with letrozole alone as a first-line treatment for postmenopausal ER-positive, HER2-negative breast cancer patients with locally advanced or metastatic disease.

Finn RS, Crown JP, Lang I, et al. Results of a randomized phase 2 study of PD 0332991, a cyclin-dependent kinase (CDK) 4/6 inhibitor, in combination with letrozole vs letrozole alone for first-line treatment of ER+/HER2- advanced breast cancer (BC). Presented at: 2012 CTRC-AACR San Antonio Breast Cancer Symposium; December 4 — 8, 2012; San Antonio, Texas. Abstract S1-6.