RESUMO
BACKGROUND: Prophylactic growth-factor therapy with granulocyte colony-stimulating factor (G-CSF) reduces the risk of febrile neutropenia (FN) in patients with breast cancer initiating myelosuppressive chemotherapy. However, little is known about the protective benefit early in the chemotherapy cycle. METHODS: To assess the relationship between G-CSF prophylaxis and incidence of FN/infection in week 1 versus beyond week 1 of the first chemotherapy cycle, a retrospective study was conducted using Medicare claims from 2005 through 2020 among patients with breast cancer initiating high-risk chemotherapy. Two cohorts were compared based on G-CSF prophylaxis within 3 days following chemotherapy initiation. The primary outcome was FN or infection, defined as hospitalization with neutropenia, fever, or infection diagnosis. Secondary outcomes were a stricter definition of FN and infection-related hospitalization. Unadjusted and regression-adjusted proportions of patients experiencing each outcome during week 1 versus beyond week 1 of the first chemotherapy cycle were compared. RESULTS: Of 78,810 patients meeting all inclusion criteria (>98% female; mean age, 69 years), 79% initiated TC (docetaxel/cyclophosphamide), 14% TCH (docetaxel/carboplatin/trastuzumab), and 7% TAC (docetaxel/doxorubicin/cyclophosphamide). Among patients receiving G-CSF (74%), incidence of first-cycle FN/infection was lower compared with patients not receiving G-CSF (overall, 6% vs 13%; TAC, 12% vs 19%; TC, 6% vs 12%; TCH, 5% vs 15%). However, patients who received G-CSF were generally more likely to experience FN/infection in week 1 (adjusted odds ratio [aOR], 1.24 for all; 1.73 for TAC; 1.35 for TC; and 0.76 for TCH). Results were similar for strictly defined FN (overall aOR, 1.29 for week 1 and 0.12 for beyond week 1) and infection-related hospitalization (overall aOR, 1.33 for week 1 and 0.27 for beyond week 1). CONCLUSIONS: Overall, the rates of chemotherapy-related FN and infection in week 1 of the first chemotherapy cycle are similar for patients receiving and not receiving G-CSF, suggesting continued risk in week 1 despite prophylactic G-CSF.