ABCG2 and neutropenia: Our observation that the ABCG2 421 AA genotype was associated with reduced risk of neutropenia (which we defined as <2000/μL being equivalent to grade 1 and above as described in CTCAE version 3.0 [32]) appears to be inconsistent with the observation of Kim et al. [20] that grade 3 or grade 4 neutropenia is significantly more common in carriers of this genotype.