The ABCB1 rs17064 heterozygous variant (AT) (OR 4.56; 1.25–16.63; p = 0.021), DPYD rs291583 allele G (OR 1.83; 1.03–3.21; p = 0.036) and positive HER2 status (OR 1.69; 0.99–2.87; p = 0.049) increased overall neutropenia risk (Table 3). This evidence concerns the gene ABCB1 and neutropenia.