Adding abemaciclib to endocrine therapy can reduce the risk of breast cancer progressing in newly diagnosed postmenopausal women, according to interim results of a Phase 3 clinical trial.
Italian researcher Angelo Di Leo presented the findings at the European Society for Medical Oncology Congress in Madrid, Sept. 8-12. The MONARCH 3 study (NCT02246621) involves hormone receptor (HR)-positive, HER2-negative advanced breast cancer.
Dr. Angelo Di Leo, a cancer specialist at the Istituto Toscano Tumori’s Hospital of Prato in Italy, made the presentation, which was titled “Abemaciclib as initial therapy for patients with HR+/HER2- advanced breast cancer.” He was the study’s lead author.
MONARCH 3 is investigating the effectiveness of a combination of abemaciclib and endocrine therapy as an initial treatment for this patient population. Abemaciclib is a cyclin-dependent kinase (CDK) 4/6 inhibitor. CDKs are molecules that regulate cell proliferation and growth, and CDK4/6 is often overactive in breast cancers, allowing cancer cells to multiply uncontrollably.
The ongoing trial involves 493 patients from 22 countries. It is randomizing participants to receive one of two combination therapies. One combo is abemaciclib and either Novartis’ Femara (letrozole) or AstraZeneca’s Arimidex (anastrozole). The other combination, which constitutes the control arm of the trial, is a placebo and either Femara or Arimidex. Twice as many patients are receiving the first combo as the second.
The study’s primary objective is to see which combo leads to longer progression-free survival — that is, the time it takes for patients’ cancer to progress.
Secondary measures of effectiveness will include patients’ overall response rate and overall survival rate. Overall response includes both complete and partial responses. Researchers will also evaluate the combo’s safety.
An interim analysis at 18 months showed that the trial met its primary objective. The combination reduced patients’ risk of disease progression or death by 46 percent, compared with endocrine therapy alone. Response rates were also higher in the combo arm — 59 percent, versus 44 percent in the control arm.
“This is the third study demonstrating that the combination of endocrine therapy with a CDK4/6 inhibitor is better than endocrine therapy alone,” Di Leo said in a press release. “Abemaciclib reduced the risk of disease progression by 46 percent.”
The team also found that the combination therapy had a more pronounced effect in patients with “more challenging disease characteristics,” such as those whose cancer had spread to the liver. The outlook for patients with slow-progressing breast cancer or with cancer that had spread to bones was excellent with endocrine therapy alone, researchers said.
“Now for the first time,we have insights suggesting that patients with certain clinical characteristics may benefit differently from treatment with a CDK 4/6 inhibitor, including the possibility that some patients with a good prognosis may be able to start on endocrine therapy alone,” Di Leo said.
In patients with a good endocrine therapy outlook, CDK 4/6 inhibitors could be reserved as a next line of treatment for breast cancer that spreads to other areas, he said. “This may be a more optimal treatment strategy for some patients since it can avoid the toxicity of first-line CDK 4/6 inhibitors and save costs.”
“Many patients with metastatic disease [one that has spread to other areas] still receive chemotherapy, despite guidelines and data from clinical trials,” said Dr. G. Curigliano, director of New Drug Development at the European Institute of Oncology. “This study confirms that we should avoid chemotherapy in hormone receptor-positive, HER2-negative metastatic breast cancer” unless there’s a critical need for it.
He said new trials should be conducted to determine the optimal treatment sequence for breast cancer patients.
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