Abstract P5-18-10: Mecapegfilgrastim for primary prophylaxis of neutropenia in 355 HER2+ breast cancer patients treated with neoadjuvant docetaxel in combination with trastuzumab and/or pyrotinib: Exploratory analysis from randomized, double-blind, phase 3 PHEDRA study

Abstract Background: A dose relationship may exist for both antitumor activity and toxicity of docetaxel in breast cancer (BC) patients, while 86% grade 4 neutropenia and 12% febrile neutropenia (FN) were reported when pretreated advanced breast cancer (ABC) patients received 100 mg/m2 docetaxel monotherapy without hematopoietic support. PHEDRA was a randomized, double-blind, multicenter, phase 3 study comparing the efficacy and safety of adding pyrotinib to trastuzumab and docetaxel as neoadjuvant treatment in women with HER2+ early or locally ABC (ClinicalTrials.gov: NCT03588091). We conducted this exploratory analysis to evaluate the effectiveness of mecapegfilgrastim, a long-acting recombinant human granulocyte colony-stimulating factor (rhG-CSF), as primary prophylaxis for neoadjuvant chemotherapy-induced neutropenia in BC patients. Methods: Patients with HER2-positive early or locally ABC were randomly assigned (1:1) to pyrotinib arm receiving 4 neoadjuvant cycles of docetaxel (100 mg/m2 iv d1 q3w), trastuzumab (8 mg/kg iv, cycle 1 d1, then 6 mg/kg d1 q3w), and pyrotinib (400 mg po qd, d1-21, q3w) or placebo arm with placebo, trastuzumab and docetaxel. Per protocol, patients were required to receive a single, 6-mg fixed dose of mecapegfilgrastim on Day 2 of each cycle. Other G-CSF was permitted if mecapegfilgrastim was unavailable at the local center or patients occurred mecapegfilgrastim intolerance. The incidence of neutropenia, FN, time to first neutropenia onset, duration per neutropenia event and cumulative neutropenia duration during neoadjuvant treatment period; and the incidences of grade 3/4 neutropenia, FN and decreased WBC count in Cycle 1 to 4 (C1-4) were presented. The data cutoff date was April 30, 2021. Results: Between July 23, 2018 and January 8, 2021, 355 patients were randomized (pyrotinib arm, n=178; placebo arm, n=177). Among them, 291 (82.0%) patients received a single, 6-mg fixed dose of mecapegfilgrastim in Cycle 1 and 270 (76.1%) patients received mecapegfilgrastim in each of the 4 cycles. Grade 3/4 neutropenia was reported in 33 (18.5%) patients in the pyrotinib arm and 36 (20.3%) patients in the placebo arm. Five (2.8%) patients in the pyrotinib arm and 2 (1.1%) patients in the placebo arm developed FN (5 FN occurred in C1; 2 FN occurred in C2). Median duration of grade 3/4 neutropenia was 3 days in the pyrotinib group and 3 days in the placebo group. Median cumulative duration of grade 3/4 neutropenia was 4 days and 3 days in the pyrotinib group and the placebo group, respectively. Grade 3/4 neutropenia mainly occurred during the first cycle of treatment for both pyrotinib (13.5%) and placebo arm (15.8%), reduced in the second cycle (5.9% vs 4.0%) and thereafter (C3: 1.8% vs 3.4%; C4: 2.4% vs 1.7%). Similar trends were observed for grade 3/4 WBC count decreased in Cycle 1 to 4. No grade 4 infection occurred. Overview of neutropenia, FN and WBC count decreased was summarized in Table 1. Consistent findings were observed in 291 mecapegfilgrastim treated patients. Conclusion: The exploratory analysis demonstrated 6-mg fixed dose of mecapegfilgrastim was effective when administrated as primary prophylaxis for neoadjuvant chemotherapy-induced neutropenia, which could be considered as a new treatment option for its advantage of once-per-cycle dosing and convenient dose management. Table 1.Overview of neutropenia, febrile neutropenia and WBC count decrease during neoadjuvant treatment period.Docetaxel+Trastuzumab+Pyrotinib(N=178)Docetaxel+Trastuzumab+Placebo (N=177)All randomized patients(N=355)Neutropenia, n (%)Any grade57 (32.0)54 (30.5)111 (31.3)Grade 16 (3.4)5 (2.8)11 (3.1)Grade 218 (10.1)13 (7.3)31 (8.7)Grade 315 (8.4)20 (11.3)35 (9.9)Grade 418 (10.1)16 (9.0)34 (9.6)Median time to first onset (IQR), days7 (6-63)6 (6-49)7 (6-53)Median duration per grade 3 or higher neutropenia, days (range)3 (1-16)3 (2-12)3 (1-16)Median cumulative duration of grade 3 or higher neutropenia, days (range)4 (2-16)3 (2-14)3 (2-16)FN, n (%)5 (2.8)2 (1.1)7 (2.0)Grade 3 or higher neutropenia, n (%) *Cycle 124 (13.5)28 (15.8)52 (14.6)Cycle 210 (5.9)7 (4.0)17 (4.9)Cycle 33 (1.8)6 (3.4)9 (2.6)Cycle 44 (2.4)3 (1.7)7 (2.1)Grade 3 or higher FN, n (%) *Cycle 12 (1.1)2 (1.1)4 (1.1)Cycle 22 (1.2)02 (0.6)Cycle 3000Cycle 4000Grade 3 or higher WBC count decreased, n (%) *Cycle 120 (11.2)20 (11.3)40 (11.3)Cycle 28 (4.7)2 (1.1)10 (2.9)Cycle 32 (1.2)1 (0.6)3 (0.9)Cycle 44 (2.4)2 (1.1)6 (1.8)Note: IQR, interquartile range; FN, febrile neutropenia; WBC, white blood cell.*The denominator indicates number of patients with mecapegfilgrastim for prophylaxis use in this cycle. Citation Format: Min He, Benlong Yang, Jiong Wu, Zhenzhen Liu, Hongjian Yang, Jinhai Tang, Kun Wang, Yunjiang Liu, Haibo Wang, Peifen Fu, Shuqun Zhang, Qiang Liu, Zefei Jiang, Shusen Wang, Jian Huang, Chuan Wang, Shu Wang, Yongsheng Wang, Linlin Zhen, Xiaoyu Zhu, Shulin Liu, Ping Yan, Jianjun Zou. Mecapegfilgrastim for primary prophylaxis of neutropenia in 355 HER2+ breast cancer patients treated with neoadjuvant docetaxel in combination with trastuzumab and/or pyrotinib: Exploratory analysis from randomized, double-blind, phase 3 PHEDRA study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-18-10.