Filgrastim-Mediated Neutrophil Recovery in Patients with Breast Cancer Treated with Docetaxel and Doxorubicin

Study Objectives. To study the impact of filgrastim 5 μg/kg given once/day through absolute neutrophil count (ANC) recovery on the duration of grade 4 neutropenia (ANC < 0.5 × 10³/mm³) and time to ANC recovery. Additional objectives were to study the average number of filgrastim injections/cycle required to achieve ANC recovery and differences in outcome by cycle. Design. Combined analysis of two double-blind, randomized, multicenter trials. Patients. Two hundred twenty-two patients treated for breast cancer. Measurements and Main Results. All patients but one were evaluable for efficacy end points. Mean ± SD duration of grade 4 neutropenia was 1.7 ± 1.3 days in cycle 1; the duration decreased in cycles 2-4 to between 1.0 and 1.2 days. Fifty percent of patients had ANC recovery to 10 ×0 10³/mm³ or greater by day 11 of the cycle, and 90% by day 13, corresponding to 10 and 12 days of filgrastim administration, respectively. Across all cycles, the mean ± SD number of filgrastim injections/cycle was 10.51 ± 1.70, with little variation among cycles. Conclusion. When filgrastim is administered as recommended, starting 24 hours after chemotherapy and continuing through an ANC of 10 × 10³/mm³ or greater, neutrophil recovery is rapid and predictable. Because the first cycle of chemotherapy has the highest rates of neutropenia and febrile neutropenia, it seems prudent to administer growth factor support preemptively.