A retrospective analysis of nadir-neutropenia directed pegylated granulocyte-colony stimulating factor on febrile neutropenia rates in (neo)adjuvant breast cancer chemotherapy regimens

Background: Pegfilgrastim, a pegylated granulocyte colony-stimulating-factor (GCSF), reduces chemotherapy morbidity and mortality in early stage breast cancer. The optimal approach to individual patient selection for GCSF is unknown, in particular whether secondary GCSF should be given after asymptomatic neutropenia, or only after febrile neutropenia (FN). Aims: To determine if preplanned nadir blood counts and subsequent nadir-neutropenia directed GCSF was effective to reduce rates of FN associated with (neo)adjuvant breast cancer chemotherapy. We also aimed to describe (neo)adjuvant chemotherapy and GCSF prescribing practices at our institution. Methods:This was a retrospective electronic medical record review. The rate of FN with secondary GCSF after cycle 1 nadir-neutropenia <1.0 × 109 cells/L was compared with the rate of FN in patients who did not have cycle 1 nadir blood counts or secondary GCSF, and analyzed according to patient and treatment data. Results:Between 11/4/2011 and 22/4/2018, 584 patients received (neo)adjuvant chemotherapy. Over all rates of FN were 17%, compared with 9% in patients who received primary GCSF. Rates of FN were highest in docetaxel/carboplatin/trastuzumab (TCH, 27%) and docetaxel/cyclophosphamide (TC, 27%). There were 268 patients (46%) who received primary GCSF and 238 patients (41%) who received secondary GCSF. Rates of FN did not differ between patients who received nadir-neutropenia directed secondary GCSF (6/125, 5%, 95% CI 1.1-8.6), and those who did not have nadir blood counts or secondary GCSF (0/49, 0%, 95% CI not calculable) (P = .1186). GCSF use was associated with lower rates of non-FN hospital admissions. Patients ≥65 years were more likely to have FN and non-FN admissions. Two of three treatment related deaths occurred due to FN. Conclusions: In this population, nadir-neutropenia directed secondary GCSF was not associated with reduced rates of FN. Observed rates of FN >20% in TC and TCH in routine clinical practice should guide primary GCSF use in accordance with international guidelines.