Efficacy and toxicity of CDK 4/6 inhibitors in real clinical practice in patients with HR+ Her2new negative metastatic breast cancer

Objective. To evaluate the efficacy and toxicity of the CDK4/6 inhibitors Palbociclib and Ribociclib in patients with HR+HER2-negative breast cancer. Material and methods. One hundred sixty-three (n=163) patients diagnosed with luminal breast cancer (BC) who received hormone-targeted therapy were included I the retrospective study. Patients were randomized into 2 groups depending on the treatment: the first group (n=79) received hormonal therapy and ribociclib, the second (n=84) received hormonal therapy and palbociclib. The primary analysis examined the objective response rate per RECIST 1.1 in each study group and the incidence and severity of adverse events using NCI CTCAE v5.0 toxicity criteria. Results. When analyzing objective responses according to RECIST 1.1, complete responses (CR) were not observed in groups, partial responses (PR) were detected in 15% (n=11) of patients in the ribociclib group and in 15% (n=13) — in the palbociclib group (p=0.7799), stabilization (SD) — in 43% (n=34) of cases in group 1 and in 48% (n=40) of cases in group 2 (p=0.5574); progression (PD) — in 25% (n=20) versus 15% (n=13) (p=0.1194), respectively. Leukopenia was observed in 8.9% (n=7) patients in the ribociclib group and in 26.2% (n=22) patients in the palbociclib group (p=0.0088). The incidence of neutropenia in the palbociclib group was 27.4% (n=23). The use of ribociclib was associated with a more frequent development of hepatotoxicity: 17.7% (n=14) versus 3.6% (n=3) of patients receiving ribociclib and palbociclib, respectively. There was no difference between the groups in the frequency of anemia and asthenia. Conclusion. The use of CDK 4/6 inhibitors in the treatment of patients with luminal Her2-negative breast cancer is effective, but the appointment of targeted therapy is associated with the development of adverse effects, which can affect the choice of drug depending on the comorbidity and initial clinical and instrumental parameters.