Positive results have been reported from a phase 3 trial of palbociclib (Ibrance, Pfizer), an oral, first-in-class inhibitor of cyclin-dependent kinases (CDKs) 4 and 6. The study met its primary endpoint by demonstrating an improvement in progression-free survival (PFS) with the combination of palbociclib and letrozole compared with letrozole plus placebo in postmenopausal women with estrogen receptor-positive (ER+), human epidermal growth factor receptor 2-negative (HER2–) advanced or metastatic breast cancer who had not received previous systemic treatment for their advanced disease.
The phase 3 PALOMA-2 trial provided confirmatory evidence for the efficacy of palbociclib in combination with letrozole in the first-line setting, which was first studied in the phase 2 PALOMA-1 trial. The new data will support a request for conversion of the accelerated approval for palbociclib to regular approval in the United States.
Based on the results of the PALOMA-1 study, palbociclib was approved by the FDA in February 2015 for the treatment of postmenopausal women with ER+/HER2– advanced breast cancer in combination with letrozole as initial endocrine-based therapy for their metastatic disease. The indication in combination with letrozole was approved under accelerated approval based on PFS. As stated at the time of the approval, continued approval for this indication may be contingent upon verification and description of a clinical benefit in the PALOMA-2 trial, which the FDA identified as the confirmatory study.
In the phase 3 PALOMA-3 trial, palbociclib was administered in combination with fulvestrant in women with hormone receptor-positive (HR+), HER2– advanced or metastatic breast cancer whose disease had progressed after endocrine therapy.
The PALOMA-1 trial was a randomized, multinational, open-label trial designed to assess PFS in postmenopausal women with ER+/HER2– advanced breast cancer receiving palbociclib (125 mg once daily for three out of four weeks in repeated cycles) in combination with letrozole compared with letrozole alone (2.5 mg once daily on a continuous regimen) as first-line treatment. The results were published in December 2014 in the online edition of Lancet Oncology.
The PALOMA-2 trial was a randomized, multinational, double-blind study designed to assess PFS in 666 postmenopausal women with ER+/HER2– advanced breast cancer receiving palbociclib (125 mg orally once daily for three out of four weeks in repeated cycles) in combination with letrozole (2.5 mg once daily continuously) compared with letrozole plus placebo as first-line treatment.
The PALOMA-3 trial was a randomized, multinational, double-blind study designed to evaluate PFS with palbociclib (125 mg once daily orally for three out of four weeks in each cycle) in combination with fulvestrant (500 mg intramuscularly on days 1 and 15 of cycle 1, and then on day 1 of each subsequent 28 day cycle) compared with fulvestrant plus placebo in pre-, peri-, and postmenopausal women with HR+/HER2– metastatic breast cancer whose disease had progressed during or after endocrine therapy. Based on the results from this study, a supplemental new drug application was approved in February 2016 to expand the use of palbociclib as part of combination therapy with fulvestrant in women with HR+/HER2– advanced or metastatic breast cancer with disease progression after endocrine therapy.
Source: Pfizer; April 19, 2016.