In conclusion, this prospective study suggests that primary pegfilgrastim prophylaxis can reduce the rate of grade 3 or 4 neutropenia/febrile neutropenia in patients with CLL receiving R-FC chemotherapy in contrast to previous studies and our historical cohort in which chemotherapy dose adjustment and infusion schedule delays occurred frequently during R-FC therapy without G-CSF prophylaxis. Here, CSF3 is linked to Decreased total neutrophil count.