Role of Cyclin-Dependent Kinase 4/6 in Metastatic Breast Cancer: Real-World Data From a Tertiary Care Institute in Eastern India.

Introduction CDK4/6 inhibitors currently approved for patients with hormone-receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer include palbociclib, ribociclib, and abemaciclib. This study aims to report on the treatment outcomes and real-world data regarding the use of CDK4/6 inhibitors in the treatment of ER+/HER2- metastatic breast cancer at a tertiary care institute in Eastern India. Materials and methods The present study is a retrospective analysis of data from patients with metastatic HR+/HER2- breast cancer who were treated with CDK4/6 inhibitors at a tertiary care institute in Eastern India between 2015 and 2022. The data were collected from online records in the departmental files and analyzed for the primary baseline characteristics of the patients, tumors, and response rates, including partial response (PR), complete response (CR), progressive disease (PD), and stable disease (SD), as defined by the Response Evaluation Criteria in Solid Tumors (RECIST) criteria version 1.1. The treatment administered, progression-free survival (PFS), and toxicity were also evaluated. Results From 2015 to 2022, 24 eligible patients were treated with CDK4/6 inhibitors for metastatic HR+/HER2- breast cancer. The average duration of follow-up was 25 months. Out of the 24 patients, 15 (62.5%) were taking Tab. ribociclib, six (25%) were taking Tab. palbociclib, and three (12.5%) were taking Tab. abemaciclib. CDK4/6 was used as a first-line therapy for 16 patients, while eight patients received it as a second-line treatment. Out of the total number of patients, six (25%) had stable disease, 13 (54.2%) had a partial response, and four (16.7%) had progressive disease. In total, of the eligible patients, five (20.8%) had grade I neutropenia, seven (29.2%) had grade II neutropenia, and four (16.7%) had grade III neutropenia. At five years, the PFS rate estimated by the Kaplan-Meier method was 50% (95% CI: 47.89-69.31). Conclusion Ribociclib and palbociclib have improved PFS in patients with metastatic HR+/HER2- breast cancer. Both drugs have well-tolerated toxicity, allowing patients to continue taking them for an extended period of time. CDK4/6 inhibitors have a higher response rate than the other agents.