The combination of CDK4/6 inhibitors plus ET was associated with increased cases of neutropenia (HR, 57.05; 95% CI, 38.26-85.05; P < .001), with low study heterogeneity (I2 = 46%; P = .07), of leukopenia (HR, 36.36; 95% CI, 19.35-68.34; P < .001), also with low heterogeneity (I2 = 0%; P = .57), and of diarrhea (HR, 4.97; 95% CI, 2.84-8.69; P < .001), with high study heterogeneity (I2 = 62%; P = .009) (eFigure 6 in the Supplement) (Table 2). This evidence concerns the gene CDK4 and Decreased total leukocyte count.