ASCO Highlights: Breast Cancer Treatments for Advanced / Metastatic Breast Cancer

Three new reports look at improving treatment for metastatic breast cancer

CDK4/6 inhibitors may offer new treatments in metastatic breast cancer. Updates from two clinical trials of CDK4/6 targeted therapies reported promising results in metastatic breast cancer. Dr. Maura Dickler (Memorial Sloan Kettering Cancer Center) reported on the MONARCH trial, a phase II single-arm study designed to evaluate safety and efficacy of the CDK4/6 inhibitor abemaciclib as monotherapy in women with hormone receptor (HR)+/HER2 negative metastatic breast cancer. Patients qualified if their disease progressed during or after endocrine therapy and chemotherapy. Dr. Dickler reported that nearly 23 percent of patients had stable disease of six months. Seven percent of patients discontinued therapy due to adverse events including diarrhea, fatigue, nausea and loss of appetite.  Commenting on the study, Dr. Dickler noted that it “confirmed single-agent activity of abemaciclib in a heavily pre-treated population with HR+/HER- metastatic breast cancer.” BCRF investigator Drs. Hope Rugo is a co-author on the study.

Nicholas Turner (Royal Marsden Hospital) reported on the PALOMA 3 study, a randomized, double-blind, phase III study comparing the CDK4/6 inhibitor palbociclib plus fulvestrant with fulvestrant alone in pre- and postmenopausal women with HR+/HER2– metastatic breast cancer whose disease had progressed on prior endocrine therapy. In addition, the study included analysis of mutations in the ESR gene. Mutations in ESR1 have been implicated in resistance to endocrine therapy in metastatic breast cancer and the researchers aimed to determine whether ESR1 mutations affect sensitivity to palbociclib. According to Dr. Turner, analysis of blood in pre- and post-menopausal PALOMA 3 patients indicates that the CDK4/6 inhibitor may be beneficial in patients whose tumors harbor ESR1 mutations. Patients receiving the combination of palbociclib plus fulvestrant had significantly better overall survival than those receiving fulvestrant alone, regardless of ESR1 status. “Because of the frequency of ESR1 mutation in this patient population,” Dr. Turner commented, “the combination of fulvestrant and palbociclib presents an attractive treatment option for ESR1 mutant cancer.”  BCFR investigators Drs. Fabrice André and Sherene Loi are co-authors on the study.

Surgery plus systemic therapy, versus systemic therapy alone, may be beneficial for women who present with breast cancer that has already metastasized at the time of initial diagnosis (called de novo MBC). Results from a multicenter phase III randomized trial reported that loco-regional surgery (LRS) followed by systemic therapy (ST) improved survival in the treatment of naïve stage IV breast cancer patients compared to systemic therapy alone. The study was conducted across 25 institutions and included 274 women newly diagnosed with advanced breast cancer. Following 40 months of follow up, the women who received local therapy to remove the primary tumor lived an average of nine months longer than women who did not receive surgery and more than 42 percent of the surgery plus systemic therapy group lived five years after diagnosis compared to 25 percent in the group receiving systemic therapy alone. Read more about the study here.

Expanding Access to Targeted Breast Cancer Treatment: Biosimilar Shows Comparable Efficacy and Safety to Trastuzumab in HER2-Positive Metastatic Breast Cancer. Biosimilars are drugs that closely mimic a biological drug, a drug that is produced from a natural source such as human, animal or micro bacteria. Examples of biologic drugs include the HER2-targeted therapy trastuzmab, a human-derived antibody. BCRF investigator, Hope Rugo reported that MYL-1401O, trastuzumab biosimilar, was equally effective as trastuzumab in a randomized phase III trial conducted at 95 sites across Asia, Latin America, Africa, and Europe.  MYL-14010 had a similar safety profile as traztuzumab and an objective response rates at 24 weeks of 70 percent compared to 64 percent with trastuzumab. Commenting on the significance of the study to the ASCO Post, Dr. Rugo noted: “Trastuzumab has markedly improved survival of women with HER2-positive breast cancer, but many women around the world can’t benefit from trastuzumab due to its high cost. We hope that the introduction of biosimilars will expand patient access to this effective drug, which has already benefited the lives of thousands of people across the globe.” Read more about the study in the ASCO Post.