The combination of the CDK4 and CDK6 inhibitor palbociclib and fulvestrant was associated with significant improvement in progression-free survival (PFS) compared with fulvestrant and placebo in patients with metastatic breast cancer.1

“The PALOMA-3 study is important for several reasons,” said Massimo Cristofanilli, MD, of the Robert H. Lurie Comprehensive Cancer Center, Northwestern University in Chicago IL, in an interview with Cancer Therapy Advisor.

“[It] demonstrated that the combination regimen…is extremely effective in patients that failed endocrine therapy, and the regimen is associated with minimal (reversible) side effects. It represents an ideal choice for second-line or even later treatment of hormone receptor-positive disease.”

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In the study, 521 women 18 years or older with hormone-receptor-positive, human epidermal growth factor (HER)2-negative metastatic breast cancer that had progressed on previous endocrine therapy were recruited between October 2013 and August 2014.

A total of 347 patients were assigned to receive fulvestrant plus palbociclib and 174 patients were assigned to receive fulvestrant plus placebo. Median PFS was 9.5 months in the study group and 4.6 months in the control group. This was the first phase 3 combination regimen study of fulvestrant and palbociclib to include premenopausal, perimenopausal, and postmenopausal women.

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These results confirmed previous findings that compared endocrine monotherapy to combination therapy.

“In my opinion, this result confirms that single-agent endocrine therapy is unlikely to benefit patients that failed or progressed during endocrine therapy,” said Dr Cristofanilli. “Using a CDK4/6 inhibitor [to] affect proliferation of cancer cells is an extremely effective strategy to overcome resistance no matter resulting from specific molecular drivers.”