Addition of ribociclib improves survival over hormone therapy alone

The addition of ribociclib, an inhibitor of the cell cycle, to standard hormone therapy significantly improved progression-free survival (PFS) in pre-menopausal patients with advanced hormone receptor-positive (HR+) breast cancer, according to results of the MONALEESA-7 Phase III clinical trial led by researchers at MD Anderson.

The trial results, presented at the 2017 San Antonio Breast Cancer Symposium by Debu Tripathy, M.D., chair of Breast Medical Oncology, also show a greater overall response rate (ORR), a delay in patient-reported quality-of-life (QOL) deterioration and manageable treatment side effects with ribociclib compared to hormone therapy alone.

Ribociclib is one of a class of drugs that inhibit cyclin-dependent kinases 4/6 (CDK4/6) – proteins necessary for progression of the cell cycle. Three CDK4/6 inhibitors have been approved by the Food and Drug Administration (FDA) for use in combination with standard hormone therapies known as aromatase inhibitors in post-menopausal women with advanced HR+ breast cancer. Previously, these patients were treated with hormone therapy alone.

“This is the first study that tells us we can reliably use CDK inhibitors in pre-menopausal patients, which represent about 20 percent of all breast cancer patients in the U.S.,” said Tripathy. “This study confirms that the benefits of these drugs are similar in both pre- and post-menopausal patients with advanced hormone receptor-positive breast cancers, and I think this will change practice.”

Pre-menopausal patients also have been treated with hormone therapy and CDK4/6 inhibitors, in addition to drugs that suppress ovarian production of estrogen, but there previously was a lack of data to confirm the utility of this approach, explained Tripathy.

The international, randomized Phase III clinical trial enrolled 672 metastatic breast cancer patients, all of whom were pre- or peri-menopausal (ceased having periods within the last year) at diagnosis with HR+, HER2-negative disease. Participants could not have had prior hormone therapy for advanced disease or more than one cycle of chemotherapy for advanced disease.

This trial is also unique in that it allowed the use of either tamoxifen or aromatase inhibitors, which can be tolerated differently in some patients, noted Tripathy.

Patients were randomized to receive either ribociclib (335) or placebo (337) in combination with tamoxifen or a nonsteroidal aromatase inhibitor (NSAI), and goserelin, an ovarian suppression drug. In the ribociclib arm, 87 patients (26%) received tamoxifen, compared with 90 patients (26.7%) in the placebo arm.

Read more about the study in the MD Anderson Newsroom.