Hormone receptor (+) HER2 (-) in metastatic breast canceraffecting the response in 1ST stage CDK 4/6 inhibitortreatment predictive and prognostic factors

AIM: Human epidermal growth factor, hormone receptor positive Due to numerous resistance mechanisms, patients with stage 2 negative breast cancer may progress to the relapse/metastatic stage despite endocrine therapy. Intracellular Cyclin D/cyclin- dependent kinase/retinoblastoma protein is one of these resistance mechanisms, and at this point in the treatment, CDK inhibitors are recommended. It was intended to assess the predictive and prognostic variables influencing CDK4/6 inhibitor therapy in patients with metastatic breast cancer in this direction. MATERIALS AND METHODS: The hospital automation system and the oncology polyclinic records were used to compile information on patients who applied to the oncology polyclinic unit of Sakarya University Training and Research Hospital between January 2020 and December 2021 and received CDK4/6 inhibitor treatment as the initial step after being diagnosed with metastatic breast carcinoma. The patient demographic information, histopathology data response status, and blood parameters at the start of treatment were entered into the excel application and statistically assessed. RESULTS: Data of 92 metastatic breast cancer patients with HR (+) / Her2 (-) were included in the study. The median age of the patients was 57.8 (min-max: 44.8-70.8). With concomitant endocrine therapy in first-line therapy, 44 (47.8%) patients received ribociclib, while 48 (52.2%) received palbociclib. Patients receiving ribociclib and palbociclib did not differ significantly between the groups evaluated in terms of histological subtype, location, concomitant endocrine therapy agent, and mortality (p=0.470; p=0.569; p=0.557; p=0.720; p=0.414, respectively). In addition, there was no significant difference between the groups in terms of response rates (p=0.222) CONCLUSION: In our investigation, which assessed the clinical and pathological markers predicting response to first-line CDK4/6 inhibitors and concurrent endocrine therapy in patients with metastatic breast cancer, no association between the variables and treatment response was discovered. Keywords: CDK 4/6 inhibitors, breast cancer, palbociclib, ribociclib