Prophylactic PEG-rhG-CSF Is Associated With Fewer Severe Neutropenic Events and Preserved Chemotherapy Delivery During Platinum-Taxane-Based Concurrent Chemoradiotherapy for Locally Advanced Cervical Cancer: A Real-World Study Using Inverse Probability of Treatment Weighting

Technical Summary: Prophylactic PEG-rhG-CSF in Locally Advanced Cervical Cancer

Problem Statement
Locally advanced cervical cancer (LACC) is typically treated with definitive concurrent chemoradiotherapy (CCRT). While intensified regimens using platinum-taxane doublets (TP-CCRT) show promise for improving disease control, they are frequently limited by severe hematologic toxicity. The overlap between radiation-induced marrow suppression (particularly in the pelvic region) and the myelotoxicity of platinum-taxane chemotherapy significantly increases the risk of grade 3–4 neutropenia and febrile neutropenia (FN). These toxicities often necessitate chemotherapy dose reductions, treatment delays, or unplanned interruptions, thereby compromising the relative dose intensity (RDI) and potentially undermining the therapeutic efficacy of the intensified regimen. Although prophylactic pegylated recombinant human granulocyte colony-stimulating factor (PEG-rhG-CSF) is known to reduce neutropenia, systematic real-world evidence regarding its impact on chemotherapy delivery metrics and composite clinical benefits in the specific context of TP-CCRT for LACC remains limited.

Methodology
This study is a single-center, retrospective, real-world cohort analysis conducted at the Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine between April 2019 and December 2021.

• Cohort: The study included 192 patients with FIGO 2018 stage IIB–IVA LACC. The primary analytic cohort (n=141) consisted of patients receiving TP-CCRT, divided into two groups based on hematologic support strategy:
  • Non-PEG Group (n=68): Received reactive short-acting rhG-CSF only upon documented myelosuppression.
  • PEG Group (n=73): Received prophylactic subcutaneous PEG-rhG-CSF (6 mg) within 24–72 hours after each chemotherapy cycle.
• Statistical Approach: To address selection bias inherent in non-randomized observational data, the authors employed Inverse Probability of Treatment Weighting (IPTW) based on propensity scores. This method balanced measured confounders (including treatment year, FIGO stage, and histologic subtype) to estimate the Average Treatment Effect (ATE).
• Endpoints:
  • Primary: A composite of grade 3–4 neutropenia or febrile neutropenia during CCRT.
  • Secondary: Other severe hematologic toxicities, chemotherapy delivery metrics (cumulative delay, failure to complete cycles, compromised delivery), and the probability of maintaining a Relative Dose Intensity (RDI) ≥ 0.85.
  • Exploratory: Overall Clinical Benefit (OCB), a composite requiring high RDI, treatment completion, absence of the primary endpoint, and objective response; and a Hematologic Toxicity Burden Index (HTBI).
• Robustness: Analyses included sensitivity checks using alternative estimators (AIPW, TMLE, Overlap Weighting), E-values for unmeasured confounding, and causal mediation analysis to explore the mechanism linking toxicity burden to treatment delivery.

Key Results
In the IPTW-weighted analysis, prophylactic PEG-rhG-CSF demonstrated significant advantages over reactive support:

• Primary Endpoint: The incidence of the composite primary endpoint (grade 3–4 neutropenia or FN) was significantly lower in the PEG group compared to the Non-PEG group (21.0% vs. 57.7%, P < 0.001). The Risk Ratio (RR) was 0.24 for grade 3–4 neutropenia and 0.41 for grade 3–4 leukopenia. The Number Needed to Treat (NNT) to prevent one primary event was 2.72.
• Chemotherapy Delivery: The PEG group experienced a mean reduction in cumulative chemotherapy delay of 5.15 days. The probability of maintaining an RDI ≥ 0.85 was significantly higher in the PEG group. Rates of any treatment delay and major delay (≥7 days) were significantly reduced.
• Efficacy and Safety: The Objective Response Rate (ORR) was comparable between groups, indicating that prophylactic support did not compromise short-term antitumor activity.
• Composite Benefit: The PEG group showed a significantly higher rate of Overall Clinical Benefit (OCB) (Weighted RR 2.33).
• Mechanistic Insights: Causal mediation analysis suggested that approximately 27.5% of the improvement in treatment delivery was mediated through the reduction of the Hematologic Toxicity Burden Index (HTBI), with the remainder attributed to direct effects.

Significance and Claims
The paper claims that in a real-world setting, prophylactic PEG-rhG-CSF is a critical supportive strategy for patients undergoing intensified TP-CCRT for LACC. Its primary significance lies in demonstrating that this intervention:

1. Substantially Reduces Toxicity: It effectively mitigates severe neutropenic events without increasing the risk of other adverse outcomes.
2. Preserves Treatment Integrity: By reducing delays and maintaining higher relative dose intensity, it addresses a major barrier to the implementation of intensified chemotherapy regimens.
3. Offers a Holistic View: The study introduces and validates composite endpoints (OCB and HTBI) that integrate safety, delivery, and efficacy, providing a more comprehensive assessment of clinical benefit than isolated toxicity or response metrics.

The authors conclude that while the short-term advantages in safety and delivery are clear, prospective multicenter studies with long-term survival endpoints (Overall Survival and Progression-Free Survival) are warranted to determine if these delivery advantages translate into survival benefits. They also note that future research should include health economic evaluations to balance the upfront cost of PEG-rhG-CSF against downstream savings from reduced hospitalizations and infections.