CDK4 and anemia (phenotype): Furthermore, patients treated with CDK4/6 inhibitors in the first-line setting had fewer grade ≥ 3 hematologic adverse events (47% vs. 67%, p = 0.020), grade ≥ 3 anemia (8% vs. 16%, p = 0.167), and grade ≥ 3 neutropenia (43% vs. 60%, p = 0.051) compared to those receiving these inhibitors in subsequent lines of therapy.