ESR1 and metastatic neoplasm: The logistic regression models revealed that none of the analyzed features were significant predictors of the likelihood of receiving chemotherapy (all p > 0.05): ER and PR expression, HER2 expression, tumor grade, Ki67 index, patient age, CDK4/6i treatment duration, time from diagnosis to CDK4/6i treatment end, time from metastatic disease diagnosis to CDK4/6i treatment end, line of treatment with CDK4/6i, stage at the time of diagnosis, presence of visceral metastases, type of CDK4/6i used, and time from CDK4/6i therapy end to chemotherapy initiation.