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(SONIA study) Endocrine therapy plus CDK 4/6 inhibition in first or second line for hormone receptor positive advanced breast cancer

Project summary

Palbociclib is a new drug, effective for women with metastasized hormone-sensitive breast cancer. It is a CDK4/6 inhibitor which inhibits cancer cell division and is combined with hormone therapy. The dilemma for the physician is whether to use it at the start or as follow-up therapy when the first hormone therapy is not effective anymore. The decision to use palbociclib as start or follow-up treatment determines the duration of the treatment and, by consequence, the involved costs and side effects for the patient.
This project, named SONIA  (Selecting the Optimal positioN of CDK4/6 Inhibitors in HR+ Advanced breast cancer), investigates the differences in effectiveness of using CDK4/6 inhibitors as start or follow-up treatment and investigates the differences in side effects for the patients and the involved costs.


The goal of this study in the effectiveness of this treatment as start or follow-up treatment and the difference in side effects and cost effectiveness. This will optimize the treatment which is to the benefit of patients.

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