A multicenter phase II trial of primary prophylactic PEG‐rhG‐CSF in pediatric patients with solid tumors and non‐Hodgkin lymphoma after chemotherapy: An interim analysis

Abstract Background Pegylated recombinant human granulocyte colony‐stimulating factor (PEG‐rhG‐CSF) can be used in pediatric patients. This study assessed the safety and efficacy of PEG‐rhG‐CSF as a primary prophylactic drug against neutropenia after chemotherapy in pediatric patients with solid tumors or non‐Hodgkin lymphoma (NHL). Patients and Methods This phase II study (between October 2020 and March 2022) enrolled pediatric patients with solid tumors or NHL treated with high‐intensity chemotherapy and with grade ≥3 myelosuppression for at least 14 days during chemotherapy. Prophylactic PEG‐rhG‐CSF was given at 100 μg/kg body weight (maximum total dosage of 6 mg) once 24–48 h following chemotherapy for two cycles. The primary endpoint was the incidence of PEG‐rhG‐CSF‐related adverse events (AEs). The key secondary endpoints were the rates of grade 3/4 neutropenia and febrile neutropenia (FN). Results This study included 160 pediatric patients with a median age of 6.22 (0.29, 18.00) years. Fifty‐eight patients (36.25%) were diagnosed with sarcoma. AEs potentially related to PEG‐rhG‐CSF included bone pain (n = 32), fatigue (n = 21), pain at the injection site (n = 21), and myalgia (n = 20). The rates of grade 3/4 neutropenia and FN during treatment were 57.28% and 29.45%, respectively. Conclusion PEG‐rhG‐CSF is well tolerated and effective in pediatric patients with solid tumors or NHL. These findings should be substantiated with further trials. Clinical Trial Registration ClinicalTrials.gov identifier: NCT04547829.


| INTRODUCTION
Myelosuppression is a common potentially life-threatening adverse effect (AE) of chemotherapy in childhood cancers. 1 Chemotherapy-induced neutropenia (CIN) is dosedependent and occurs in 26%-45% of treated individuals. 2,3 CIN is associated with high morbidity and mortality in children. 3 Moreover, CIN can lead to chemotherapy interruption and dose adjustments, affecting the treatment outcomes. 4 Recombinant human granulocyte colony-stimulating factor (rhG-CSF) is commonly used for reversing CIN, 5,6 but rhG-CSF requires daily injections, affecting the compliance of pediatric patients. Polyethylene glycol conjugation (PEGylation) involves the covalent attachment of a 20-kDa PEG moiety to the N-terminal methionine residue of rhG-CSF to prolong its half-life and activity. 7 Therefore, the plasma half-life of PEG-rhG-CSF could be extended to up to 47 h, with preserved solubility, bioavailability, and stability. 8 Previous studies demonstrated its cost-effectiveness, safety, and comparable efficacy to conventional rhG-CSF for the management of CIN in adults, 9 children, and adolescents. 10,11 Pegfilgrastim, a PEGylated form of rhG-CSF (analog of filgrastim), was approved for use in children to reverse CIN and reduce the incidence of neutropenia-associated infections. 12,13 Although PEG-rhG-CSF (Brand name, Jinyouli) was approved for marketing in China in March 2012, its use has been limited to Chinese adults. In addition, the safety and efficacy of PEG-rhG-CSF (Jinyouli) in Chinese children receiving chemotherapy have not been broadly evaluated. Nevertheless, a previous study assessed the pharmacokinetics and pharmacodynamics of PEG-rhG-CSF (Jinyouli) in pediatric patients with acute lymphoblastic leukemia, providing some evidence supporting this treatment strategy in clinical practice. 14 Therefore, this prospective multicenter phase II study aimed to examine the safety and efficacy of PEG-rhG-CSF as a primary prophylactic drug for neutropenia in pediatric patients with solid tumors or non-Hodgkin lymphoma (NHL).

| Study design and patients
This prospective study enrolled pediatric cancer patients receiving high-intensity chemotherapy resulting in grade ≥3 myelosuppression (determined by the investigators) in five clinical centers between October 2020 and March 2022.
This study was approved by the Ethics Committee of the Cancer Center of Sun Yat-sen University (approval number: B2020-202-01). Informed consent was provided by each participant or their legal guardian. This trial was registered (Clini calTr ials.gov NCT04547829).

| Treatment
Two cycles of chemotherapy were administered as the primary cancer treatment, and PEG-rhG-CSF [CSPC Baike (Shandong) Biopharmaceutical Co., Ltd., Shandong, China] was administered once 24-48 h after each cycle of chemotherapy as a prophylactic drug against neutropenia. The dosage was 100 μg/kg, not exceeding 6 mg. After total WBC recovered to >2 × 10 9 /L, neutrophil count to >0.8 × 10 9 /L, and platelet count to >80 × 10 9 /L, the subsequent course of chemotherapy was resumed. In case these values were not reached, a period of 7 days was allowed for the parameters to return to normal. If the above conditions were still not reached during the 7-day period, the participants were withdrawn from the study.

K E Y W O R D S
chemotherapy, febrile neutropenia, lymphoma, pediatric cancer, pegylated granulocyte colonystimulating factor performance status score assessments were carried out 1 day before chemotherapy initiation. Subsequently, a routine blood examination was performed every other day following PEG-rhG-CSF treatment in each cycle until ANC was >0.5 × 10 9 /L. Delays in chemotherapy and dose adjustments were recorded.
The times from start to end for AEs as well as their severity, were also recorded. All participants underwent a safety assessment at the end of treatment.

| Endpoints
The primary study endpoint was the incidence and severity of drug-related AEs. Bone pain was scored daily by two scoring methods. [15][16][17] In participants aged 8 years and over, the Wong-Baker's facial pain rating scale (WBFPRS) was applied for pain assessment; in those below 8, the Face, Legs, Activity, Cry, and Consolability (FLACC) scale was used.
The secondary endpoints were the incidence rate of grade 3/4 neutropenia in each chemotherapy cycle, ANC changes in each chemotherapy cycle, occurrence, and duration of febrile neutropenia (FN) in each chemotherapy cycle (axillary temperature was utilized as standard body temperature, and FN was defined as ANC <0.5 × 10 9 /L and axillary temperature >38°C), the lowest neutrophil count in each chemotherapy cycle, the incidence of chemotherapy delays or dose adjustments in each chemotherapy cycle, the proportion of participants administered antibiotics in all chemotherapy cycles, and the incidence rates and severity of AEs.
The AEs were assessed according to the National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. AEs occurring after treatment with the study drug, including symptoms, disease course, and laboratory abnormalities, were reported. The correlation between the study drug and AE occurrence was evaluated by the physicians according to a 5point scale.
In this study, subgroup analysis was performed to examine the differences in the incidence rates of grade 3/4 neutropenia and FN for different tumor types.

| Statistical analysis
The full analysis set (FAS) included all participants who received the study drug at least once, with at least one efficacy evaluation available. The safety set (SS) included participants who received the study drug at least once, with safety assessments available after receiving the study drug.
Statistical analysis was performed with SPSS 19.0 (IBM, Armonk, NY, USA). Continuous data were presented as means ± standard deviations or medians (minimum, maximum) according to the distribution (normal or not). Categorical data were presented as n (%).

| Patient clinicodemographic characteristics
This study enrolled 166 participants, of whom two did not meet the inclusion criteria, and four did not complete the study. Eventually, 160 participants who completed the study treatment were included in the FAS and SS analyses ( Figure 1).
Pain intensity was the highest the day after injection and decreased by 2.15-fold (FLACC score, 0.71 vs. 0.33; n = 177) or 2.68-fold (WBFPRS score, 1.61 vs. 0.60; n = 126) on day 5 (Figure 2). A similar trend in bone pain decrease was found in the days after injection in the different age groups.

| Efficacy analysis
ANC peaked at 1 and 11 days after PEG-rhG-CSF treatment. ANC recovery occurred on average at 5.00 (1.00, 19.00) days in the first cycle and 4.00 (1.00, 14.00) in the second cycle (Table S3). Grade 3/4 neutropenia was observed in each chemotherapy cycle (Table S2).
Overall, the incidence of FN in all cycles was 29.45%. Seventy-two (45.00%) patients had FN in the first cycle, and this number was reduced in the second cycle (19/149, 12.75%) (Table S2), for median durations of 3 and 2 days in the first and second cycles, respectively (Table S4). The incidence rates of grade 3/4 neutropenia and FN for different tumor types are shown in Tables S5 and S6. Patients with sarcoma and neuroblastoma had the highest incidence rates of grade 3/4 neutropenia and FN.
Chemotherapy delays occurred in two participants; treatment delay was due to an unrelated condition (bed shortage) in one patient, and the second case had hydrocephalus and required cerebrovascular outflow treatment and nutritional supplementation. No dose adjustment was needed.
Sixty-six(41.25%) participants received antibiotics during myelosuppression in a total of 77 cycles, accounting for 24.92% (77/309) of all cycles. The participants were administered antibiotics for a therapeutic purpose (Table S7).

| DISCUSSION
Pegfilgrastim is a PEG-rhG-CSF approved in the United States, but the documented evidence was based on very small sample size. 18,19 Only a few studies have reported its safety in Chinese patients. 14,18 In this study, PEG-rhG-CSF (Jinyouli) was given to 160 pediatric patients and administered high-intensity chemotherapy as primary prophylaxis. A low overall incidence of drug-related AEs was determined. To the best of our knowledge, this is the first prospective study of PEG-rhG-CSF performed in a large sample of Chinese pediatric patients with various solid tumors and lymphoma and showing promising outcomes after administration.
In previous studies, the main adverse reactions after PEG-rhG-CSF administration in adult and pediatric patients included bone pain, myalgia, fever, and fatigue. [20][21][22][23][24][25] In this study, no new safety signals were found, and AEs were comparable to those described in previous studies. The occurrence of bone and/or muscle pain is most likely attributed to the primary pharmacological effect of rhG-CSF itself on the bone marrow 26 and is likely not associated with PEGylation. 27 The incidence of bone pain was slightly higher in the present study compared with a previous report, 20 in which four out of 28 treated pediatric patients (median age, 14.5 years; range, 12-18 years) had bone pain. The participants in the present study were relatively younger (6.22 years, ranging from 0.29 to 18.00 years; 68 patients <5 years of age). In a previous large phase II study, 28 13 of the 38 enrolled patients were younger than 5 years. The present study further validates the safety and efficacy of PEG-rhG-CSF (Jinyouli) in young children. The slightly higher incidence of bone pain in this study than in previous reports may also be attributed to bone marrow development in young children.
The incidence and duration of severe neutropenia with PEG-rhG-CSF (Jinyouli) were comparable to pegfilgrastim in pediatric patients with sarcoma 29 or after autologous peripheral blood stem cell transplantation. 30 In a total of 218 cycles in the present study, the rate of FN following PEG-rhG-CSF (Jinyouli) administration (29.45%) was similar to that of children who received PEG-rhG-CSF (21.4%) for a total of 196 cycles. 19 While no dose adjustments were performed due to neutropenia, chemotherapy was delayed in only two cases (2.1%), neither of which was associated with FN, which was fewer than in a previous study (9.4%). 20 Drug efficacy differed in the present study by tumor type. Most patients in this study had sarcoma (n = 58), and FN in all cycles was found in 34 (35.51%) individuals, which was much less than reported for 25/37 patients (68%) with pegfilgrastim-treated pediatric sarcoma after chemotherapy. 28 Bone marrow suppression after high-intensity chemotherapy for childhood tumors is the most common complication. PEG-rhG-CSF has the following advantages over rhG-CSF. First of all, it reduces the number of injections, thereby reducing pain in pediatric patients and improving compliance. Secondly, compared with rhG-CSF, PEG-rhG-CSF has a lower neutropenia rate in the subsequent chemotherapy cycle. 31 Finally, the cost-effectiveness of PEG-rhG-CSF for primary prevention is better than for secondary prevention because of the advantage of lowering FN incidence. 32 This study has limitations. This study included patients with different tumor types and high-intensity chemotherapy regimens. The sample size is too small, and the variability in cancers and chemotherapy regimens is too wide to allow any meaningful subgroup analysis.
In conclusion, prophylactic PEG-rhG-CSF can be used in pediatric cancer patients. The present study suggests that PEG-rhG-CSF injection is convenient, safe, and effective in pediatric patients with cancer receiving highintensity chemotherapies. Future studies are warranted

ACKNOWLEDGMENTS
The authors thank the children and their families for agreeing to participate in the study, as well as Huazhen Chen for developing the study database. We sought assistance from a professional English Language editing service from American Journal Experts.

FUNDING INFORMATION
The study was supported by CSPC Baike (Shandong) Biopharmaceutical Co., Ltd.

CONFLICT OF INTEREST STATEMENT
The authors declare no conflict of interest.

DATA AVAILABILITY STATEMENT
All original data were deposited online http://www.resea rchda ta.org.cn.