Impact of Primary Prophylactic Pegfilgrastim for Febrile Neutropenia on Dose Intensity of Adjuvant Docetaxel Therapy in Patients with Breast Cancer: A Single-Center Retrospective Cohort Study

Docetaxel (DOC) is a key therapeutic agent for patients with breast cancer in both the adjuvant and neoadjuvant settings. In the adjuvant setting, maintaining dose intensity is important for improving patient outcomes. The aim of this study was to evaluate whether primary prophylaxis with pegfilgrastim (PEG) for febrile neutropenia improves average relative dose intensity (ARDI). This single-center, retrospective, observational cohort study included patients with breast cancer who received DOC in either the adjuvant or neoadjuvant setting at Keiyu Hospital between April 2021 and March 2025. Exclusion criteria included DOC dose reduction during the first treatment cycle, co-administration of other cytotoxic agents, absence of prior anthracycline treatment, and loss to follow-up. The primary outcome was the mean difference (MD) in the ARDI of DOC, whereas the secondary outcomes were the incidence of febrile neutropenia and the reasons for DOC discontinuation or dose reduction. The PEG and non-PEG groups comprised 31 and 65 patients, respectively. After adjustment using inverse probability of treatment weighting, the ARDI values were 94.43％ and 95.09％ in the PEG and non-PEG groups, respectively. The adjusted MD in ARDI was -0.65％ (95％ confidence interval, -4.12 – 2.81). In conclusion, this study found no statistically significant difference in ARDI between patients who received primary prophylaxis with PEG and those who did not. Given the retrospective observational design and exploratory nature of this study, these findings should be interpreted cautiously. Further studies are needed to clarify the role of primary PEG prophylaxis in maintaining DOC dose intensity.