Real-world effectiveness of mecapegfilgrastim for prophylaxis in patients with breast cancer receiving 2-weekly and 3-weekly chemotherapy in China

Breast cancer patients receiving myelosuppressive chemotherapy are at high risk of febrile neutropenia (FN). Long-acting G-CSFs are recommended for FN prevention, but evidence for mecapegfilgrastim in the dose-dense setting remains limited. This multicenter, prospective, observational, real-world study was conducted at 43 centers in China. Patients with breast cancer who received 2-weekly or 3-weekly chemotherapy with mecapegfilgrastim (6 mg) as prophylaxis for chemotherapy-induced neutropenia were enrolled. The primary outcome was the incidence of FN, defined as an oral temperature of > 38.3 °C or two consecutive readings of > 38.0 °C for 2 h and an absolute neutrophil count (ANC) of < 0.5 × 10 9 /l, or expected to fall below 0.5 × 10 9 /L. The secondary outcomes included severe neutropenia and adverse events (AEs). Between June 2019 and March 2022, a total of 757 patients were enrolled. After 1:2 propensity score matching, 36 patients were included in the 2-weekly group and 71 patients were included in the 3-weekly group. In the first cycle, FN, grade 3/4 neutropenia, and grade 4 neutropenia occurred in 0 (0%; 95% CI, 0.0-9.6%), 9 (25.0%; 95% CI, 13.8–41.1%), and 4 (11.1%; 95% CI, 4.4–25.3%) patients in the 2-weekly group, and in 2 (2.8%; 95% CI, 0.8–9.7%), 11 (15.5%; 95% CI, 8.9–25.7%), and 5 (7.0%; 95% CI, 3.0-15.4%) patients in the 3-weekly group. Across all cycles, the corresponding incidences were observed in 0 (0.0%), 11 (30.6%), and 5 (13.9%) patients in the 2-weekly group, and 2 (2.8%), 14 (19.7%) and 7 (9.9%) patients in the 3-weekly group. Dose hold (≥ 5 days) occurred in 7 patients (19.4%) in the 2-weekly group and 5 patients (7.0%) in the 3-weekly group. The incidence of grade 3/4 treatment-emergent adverse events (TEAEs) was 26.7% in the 2-weekly and 33.3% in the 3-weekly groups. No patients had serious AEs in either group. No treatment-related deaths were reported. Mecapegfilgrastim was associated with a low incidence of FN and manageable safety profiles in patients with breast cancer receiving 3-weekly or 2-weekly chemotherapy. Nevertheless, further studies with larger sample sizes are warranted to confirm these findings.