Abstract
Patients with hormone-receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer constitute about 70% of the breast cancer population. About 35% of these patients develop distant metastases and their treatment will be palliative. Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors were shown to significantly improve the outcomes of these patients. In combination with endocrine therapy, they have become the standard first-line treatment for HR-positive, HER2-negative breast cancer. In Poland, treatment with CDK4/6 inhibitors is reimbursed only for patients participating in the drug program of the Ministry of Health. However, fulfilling the eligibility criteria for the program may be challenging both for patients and for clinicians. This may lead to a delay in treatment with CDK4/6 inhibitors or a decision to use older and less effective drugs that are more widely available. The aim of this review was to compare the efficacy of first-line therapies in patients with HR-positive, HER2-negative metastatic breast cancer depending on the use of CDK4/6 inhibitors. We compared the efficacy of previous standard therapies with that of ribociclib, a CDK4/6 inhibitor, based on the median progression-free survival (PFS) as an outcome. Median PFS is not affected by the efficacy of subsequent treatment lines and is easy to interpret both for clinicians and for patients. The first-line treatment with chemotherapy or endocrine therapy (without CDK4/6 inhibitors) prolongs median PFS by several months and even to over a dozen months. The first-line treatment with endocrine therapy plus CDK4/6 inhibitors provides an opportunity to achieve a median PFS of more than 25 months and to prolong it by about 9 to 14 months.