Ribociclib improves progression free survival (PFS) in premenopausal women with hormone receptor-positive, HER2-negative advanced or metastatic breast cancer, according to a study presented at the 2018 Miami Breast Cancer Conference (March 8-11, 2018).

Ribociclib is currently approved by the FDA for use in combination with an aromatase inhibitor for the frontline treatment of postmenopausal women with hormone receptor–positive, HER2-negative advanced breast cancer.

Researchers conducted a large randomized trial (MONALEESA-7) focusing on premenopausal women with advanced breast cancer. The trial randomized patients to receive either the CDK4/6 inhibitor ribociclib in combination with tamoxifen or a nonsteroidal aromatase inhibitor (NSAI) plus goserelin, or to endocrine treatment plus goserelin. Patient characteristics were balanced between the two groups.

The regimen consisted of daily oral administration of ribociclib at 600 mg; tamoxifen at 20 mg, or letrozole at 2.5 mg, or anastrozole at 1 mg; and a subcutaneous injection of goserelin at 3.6 mg once every 28 days. Ribociclib treatment was administered for 3 weeks followed by 1 week off.

Researchers noted that prior neoadjuvant or adjuvant endocrine therapy was reported for 37.9% of patients, 14% had prior chemotherapy for advances disease, 41.2% had prior neoadjuvant or adjuvant chemotherapy, and 44.8% had no prior chemotherapy. At baseline, the disease-free interval was less than or equal to 12 months for 6.9% of patients and greater than 12 months for 52.5% of patients.

Results showed the PFS benefit with ribociclib was similar when the CDK4/6 inhibitor was combined with either tamoxifen or an NSAI. For the 87 patients receiving ribociclib/tamoxifen, the median PFS was 22.1 months compared with 11.0 months for the 90 patients treated with tamoxifen plus placebo. Among the 248 patients treated with ribociclib plus an NSAI, the median PFS was 27.5 months compared with 13.8 months for patients receiving an NSAI plus placebo.

Researchers reported the ribociclib PFS benefit was also consistent across other prespecified subgroups—age, race, ECOG performance status, ER/PgR status, liver and/or lung involvement, bone-only disease, prior chemotherapy for advanced, and disease-free interval.

Patient-reported outcomes showed that ribociclib was associated with a statistically significant improvement in time to deterioration, as well as a durable, clinically meaningful reduction in pain score as early as 8 weeks after initiation.

Neutropenia was the most frequently reported adverse event for both the experimental arm (76%) and the placebo arm (8%) in updated safety results. The most common grade 3/4 adverse events in patients receiving ribociclib combination therapy compared with endocrine therapy alone were neutropenia (60.6% vs 3.6%) and leukopenia (14.3% vs 1.2%).—Janelle Bradley