In patients who experienced grade III–IV neutropenia, the UGT1A1*6, UGT1A7*3 and UGT1A9*22 polymorphisms showed significant associations only among those who received the weekly regimen (p = 0.015, p = 0.042, and p = 0.024, respectively). Here, UGT1A9 is linked to Decreased total neutrophil count.