Study to Investigate the Optimal Duration of Treatment with CDK4/6 Inhibitors in Advanced Breast Cancer (Metastases)

A common characteristic of breast cancer cells is the presence of hormone receptors on their surface. About 70 percent of all breast cancer patients have a hormone receptor-positive tumor. This means that female hormones such as estrogen promote cancer growth by binding to the tumor cells. For this reason, medications are used that specifically prevent the release of these hormones or block the hormone receptors. Follow-up treatment (adjuvant therapy) for the disease after initial chemotherapy and surgery therefore often consists of anti-hormone therapy, as this can help eliminate any remaining tumor cells. If the cancer has spread throughout the body (metastasized), the goal of treatment is to “keep the disease in check” for as long as possible. As a result, patients are increasingly able to live for many years with a good quality of life. In advanced cases, antihormonal therapy—using medications such as fulvestrant, tamoxifen, or aromatase inhibitors—is considered the standard of care following surgery for postmenopausal patients. In addition to this antihormonal therapy, it is now common to immediately combine it with another medication—a CDK4/6 inhibitor—which can enhance the effect of the antihormonal therapy. Medications in this class include palbociclib and abemaciclib. These medications are already part of the standard of care.

The DISCUSS study aims to gather data on when additional treatment with CDK4/6 inhibitors can be discontinued while continuing anti-hormonal therapy, without causing any harm to patients as their disease progresses. The goal is to minimize the treatment regimen and potential side effects as much as possible. To this end, patients will be randomly assigned to two groups. After 12 months of anti-hormone therapy plus CDK4/6 inhibitors, in the experimental arm of the study only the anti-hormone treatment will continue without CDK4/6 inhibitors, while in the other arm, patients will continue taking both medications without change. The patients are then monitored over a 12-month period to see if the tumor progresses. The two groups are compared, and researchers assess whether continuing the combination of both medications provides a benefit. The total follow-up period is 4.5 years.

Postmenopausal patients aged 18 and older who have hormone receptor-positive, HER2-negative metastatic (stage 4) breast cancer are eligible to participate in the study. The metastases must not be located in the brain. The disease must have been controlled with combination therapy (anti-hormone therapy and CDK4/6 inhibitors) for at least 12 months—that is, it must have either completely regressed, partially regressed, or remained stable.