Endpoint surrogacy in oncological randomized controlled trials with immunotherapies: a systematic review of trial-level and arm-level meta-analyses

Objective response rate and progression-free survival as surrogates for overall survival treatment effect: A meta-analysis across diverse tumour groups and contemporary therapies

BACKGROUND

Overall survival (OS) results from randomized control trials (RCT) provide the strongest evidence for efficacy of anti-cancer treatments but can take a considerable amount of time to mature. Progression free survival (PFS) and objective response rate (ORR) are used as an early surrogate of OS treatment effect however their validity remains unclear. Our study aims to comprehensively evaluate ORR and PFS as surrogates for OS treatment effect across tumor groups and treatment types.

MATERIAL AND METHODS

Phase 3 RCTs in solid malignancies that reported OS/PFS and ORR published between 1st of January 2010 and 30th of June 2022 were evaluated. The relationship of surrogate endpoints and OS treatment effect was assessed via weighted linear regression. The coefficient of determination (R2) quantified the fit of the regression model.

RESULTS

675 phase 3 RCT comprising of 350 112 patients were analysed. ORR (R2 of 0.10) and PFS (R2 of 0.38) were poor surrogate markers of OS treatment effect. The strength of surrogacy differed within treatment and tumour groups. PFS had the highest R2 for chemotherapy (0.56) and lowest for targeted therapy (0.40). PFS had the highest level of surrogacy for melanoma (R2 = 0.72) and pancreatic cancer (R2 = 0.70) compared to other tumour groups. Importantly ORR and PFS were also poorly correlated to each other (R2 = 0.33).

CONCLUSIONS

ORR and PFS were poor trial-level surrogate markers of OS. The surrogacy performance of ORR and PFS differed by treatment and malignancy sub-type.

Time to deterioration of patient-reported outcomes as a surrogate of overall survival: a meta-analysis

BACKGROUND

Overall survival is the optimal marker of treatment efficacy in randomized clinical trials (RCTs) but can take considerable time to mature. Progression-free survival (PFS) has served as an early surrogate of overall survival but is imperfect. Time to deterioration in quality of life (QOL) measures could be a surrogate for overall survival.

METHODS

Phase 3 RCTs in solid malignancies that reported overall survival, PFS, and time to deterioration in QOL or physical function published between January 1, 2010, and June 30, 2022, were evaluated. Weighted regression analysis was used to assess the relationship between PFS, time to deterioration in QOL, and time to deterioration in physical function with overall survival. The coefficient of determination (R2) was used to quantify surrogacy.

RESULTS

In total, 138 phase 3 RCTs were included. Of these, 47 trials evaluated immune checkpoint inhibitors and 91 investigated non-immune checkpoint inhibitor agents. Time to deterioration in QOL (137 RCTs) and time to deterioration in physical function (75 RCTs) performed similarly to PFS as surrogates for overall survival (R2 = 0.18 vs R2 = 0.19 and R2 = 0.10 vs R2 = 0.09, respectively). For immune checkpoint inhibitor studies, time to deterioration in physical function had a higher association with overall survival than with PFS (R2 = 0.38 vs R2 = 0.19), and PFS and time to deterioration in physical function did not correlate with each other (R2 = 0). When time to deterioration in physical function and PFS are used together, the coefficient of determination increased (R2 = 0.57).

CONCLUSIONS

Time to deterioration in physical function appears to be an overall survival surrogate measure of particular importance for immune checkpoint inhibitor treatment efficacy. The combination of time to deterioration in physical function with PFS may enable better prediction of overall survival treatment benefit in RCTs of immune checkpoint inhibitors than either PFS or time to deterioration in physical function alone.

Association between age and efficacy of first-line immunotherapy-based combination therapies for mRCC: a meta-analysis

Aim: To compare the efficacy of first-line immune checkpoint inhibitor (ICI)-based combinations in metastatic renal cell carcinoma (mRCC) patients stratified by chronological age. Methods: According to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, hazard ratios for overall survival (OS) from randomized controlled trials were synthesized. Results: Five RCTs were eligible for meta-analyses. ICI-based combinations significantly improved OS compared with sunitinib alone, both in younger (<65 years) and older (≥65 years) patients, whereas the OS benefit was significantly better in younger patients (p = 0.007). ICI-based combinations did not improve OS in patients aged ≥75 years. Treatment rankings showed age-related differential recommendations regarding improved OS. Conclusion: OS benefit from first-line ICI-based combinations was significantly greater in younger patients. Age-related differences could help enrich shared decision-making.

Trial Design for Cancer Immunotherapy: A Methodological Toolkit

Immunotherapy with checkpoint inhibitors (CPIs) and cell-based products has revolutionized the treatment of various solid tumors and hematologic malignancies. These agents have shown unprecedented response rates and long-term benefits in various settings. These clinical advances have also pointed to the need for new or adapted approaches to trial design and assessment of efficacy and safety, both in the early and late phases of drug development. Some of the conventional statistical methods and endpoints used in other areas of oncology appear to be less appropriate in immuno-oncology. Conversely, other methods and endpoints have emerged as alternatives. In this article, we discuss issues related to trial design in the early and late phases of drug development in immuno-oncology, with a focus on CPIs. For early trials, we review the most salient issues related to dose escalation, use and limitations of tumor response and progression criteria for immunotherapy, the role of duration of response as an endpoint in and of itself, and the need to conduct randomized trials as early as possible in the development of new therapies. For late phases, we discuss the choice of primary endpoints for randomized trials, review the current status of surrogate endpoints, and discuss specific statistical issues related to immunotherapy, including non-proportional hazards in the assessment of time-to-event endpoints, alternatives to the Cox model in these settings, and the method of generalized pairwise comparisons, which can provide a patient-centric assessment of clinical benefit and be used to design randomized trials.

Immune-related adverse events as potential surrogates of immune checkpoint inhibitors' efficacy: a systematic review and meta-analysis of randomized studies

BACKGROUND

Immune-related adverse events (irAEs) are frequently reported during immune checkpoint inhibitor (ICI) therapy and are associated with long-term outcomes. It is unknown if the irAE occurrence is a valid surrogate of ICIs' efficacy.

METHODS

We identified articles reporting the results of randomized trials of experimental ICI therapy in solid tumors with a systematic search. The control arms could be placebo, cytotoxic/targeted therapy, or ICI therapy. We extracted the hazard ratios for overall survival (OS) with the number of OS events per arm and the number and percentages of overall and specific irAEs of grade 1-2 and grade 3-4 per arm. We estimated the treatment effect on the potential surrogate outcome with the odds ratio of the irAE rate between the experimental and the control arm. The statistical analysis consisted of weighted linear regression on a logarithmic scale between treatment effects on irAE rate and treatment effects on OS.

RESULTS

Sixty-two randomized trials were included for a total of 79 contrasts and 42 247 patients. The analyses found no significant association between the treatment effects for overall grade 1-2 or grade 3-4 irAE rates or specific (skin, gastrointestinal, endocrine) irAE rates. In the non-small-cell lung cancer (NSCLC) trial subset, we observed a negative association between treatment effects on overall grade 1-2 irAEs and treatment effects on OS in studies with patients selected for programmed death-ligand 1 expression (R² = 0.55; 95% confidence interval 0.20-0.95; R = -0.69). In the melanoma trial subset, a negative association was shown between treatment effects on gastrointestinal grade 3-4 irAEs and treatment effects on OS in trials without an ICI-based control arm (R² = 0.77; 95% confidence interval 0.24-0.99; R = -0.89).

CONCLUSIONS

We found low-strength correlations between the ICI therapy effects on overall or specific irAE rates and the treatment effects on OS in several cancer types.

Surrogate Endpoints as Predictors of Overall Survival in Metastatic Urothelial Cancer: A Trial-level Analysis

Background

Surrogate endpoints (SEs), such as progression-free survival (PFS) and objective response rate (ORR), are frequently used in clinical trials. The relationship between SEs and overall survival (OS) has not been well described in metastatic urothelial cancer (MUC).

Objective

We evaluated trial-level data to assess the relationship between SEs and OS. We hypothesize a moderate surrogacy relationship between both PFS and ORR with OS.

Design setting and participants

We systematically reviewed phase 2/3 trials in MUC with two or more treatment arms, and report PFS and/or ORR, and OS.

Outcome measurements and statistical analysis

Linear regression was performed, and the coefficient of determination (R²) and surrogate threshold effect (STE) estimate were determined between PFS/ORR and OS.

Results and limitations

Of 3791 search results, 59 trials and 62 comparisons met the inclusion criteria. Of the 53 trials that reported PFS, 31 (58%) reported proportional hazard regression for PFS and OS. Linear regression across trials demonstrated an R² of 0.60 between hazard ratio (HR) for PFS (HR^PFS) and HR for OS (HR^OS), and an STE of 0.41. Linear regression of ΔPFS (median PFS in months of the treatment arm - that of the control arm) and ΔOS demonstrated an R² of 0.12 and an STE of 14.1 mo. Thirty trials reported ORRs. Linear regression for ORR^ratio and HR^OS among all trials found an R² of 0.08; an STE of 95% was not reached at any value and ΔORR and HR^OS similarly demonstrated a poor correlation with an R² value of 0.03.

Conclusions

PFS provides only a moderate level of surrogacy for OS; An HR^PFS of ≤0.41 provides 95% confidence of OS improvement. ORR is weakly correlated with OS and should be de-emphasized in MUC clinical trials. When PFS is discussed, proportional hazard regression should be reported.

Patient summary

We examined the relationship between surrogate endpoints, common outcomes in clinical trials, with survival in urothelial cancer trials. Progression-free survival is moderately correlated, while objective response rate had a poor correlation with survival and should be de-emphasized as a primary endpoint.

Validating ORR and PFS as surrogate endpoints in phase II and III clinical trials for NSCLC patients: difference exists in the strength of surrogacy in various trial settings

OBJECTIVE

This study aims to systematically validate the performance of surrogate endpoints in phase II and III clinical trials for NSCLC patients under various trial settings.

METHODS

A literature search retrieved all registered phase II and III trials of NSCLC patients in which OS, with at least one of ORR and PFS, were reported. Associations between surrogate and true endpoints were assessed on two levels. On the arm level, three pairs of correlations, i.e., ORR vs. median OS, ORR vs. median PFS, and median PFS vs. median OS, were analysed using Spearman's rho. On the trial level, similarly, three pairs of correlations, i.e., ΔORR vs. HR of OS, ΔORR vs. HR of PFS, and HR of PFS vs. HR of OS, were analysed using Spearman's rho and weighted linear regression model respectively. Finally, sensitivity analyses were performed to explore surrogacy under various trial settings.

RESULTS

At arm level, three pairs of correlations are all high (Spearman's rho = 0.700, 0.831, 0.755, respectively). At trial level, there is a low correlation between ΔORR and HR of OS, a high correlation between ΔORR and HR of PFS and a moderate correlation between HR of PFS and HR of OS (Spearman's rho = 0.462, 0.764, 0.584, respectively). In the sensitivity analysis, we find correlations between surrogate and true endpoints vary by different trial settings. It is noteworthy that the strength of surrogacy of these intermediate endpoints in targeted therapy is greater than that in immunotherapy.

CONCLUSION

According to the arm-level and trial level-analysis, we suggest that in phase II and III trials of targeted therapy and immunotherapy for NSCLC patients: 1) ORR lacks validity for the surrogacy of OS, excluding in first-line therapy, and 2) ORR may be an appropriate surrogate endpoint for PFS, and 3) PFS may be considered a modest surrogacy for OS, with better performance in first-line therapy trials. Moreover, to provide more convincing evidence of surrogacy of the surrogate endpoints, patient-level analyses are in desperate need.

Correlations between objective response rate and survival-based endpoints in first-line advanced non-small cell lung Cancer: A systematic review and meta-analysis

INTRODUCTION

The study objective was to estimate the relationship between objective response and survival-based endpoints by drug class, in first-line advanced non-small cell lung cancer (aNSCLC).

MATERIALS AND METHODS

A systematic literature review identified randomized controlled trials (RCTs) of first-line aNSCLC therapies reporting overall survival (OS), progression-free survival (PFS), and/or objective response rate (ORR). Trial-level and arm-level linear regression models were fit, accounting for inclusion of immunotherapy (IO)-based or chemotherapy-only RCT arms. Weighted least squares-based R² were calculated along with 95% confidence intervals (CIs). For the main trial-level analysis of OS vs. ORR, the surrogate threshold effect was estimated. Exploratory analyses involved further stratification by: IO monotherapy vs. chemotherapy, dual-IO therapy vs. chemotherapy, and IO + chemotherapy vs. chemotherapy.

RESULTS

From 17,040 records, 57 RCTs were included. In the main analysis, trial-level associations between OS and ORR were statistically significant in both the IO-based and chemotherapy-only strata, with R² estimates of 0.54 (95% CI: 0.26-0.81) and 0.34 (0.05-0.63), respectively. OS gains associated with a given ORR benefit were statistically significantly larger within IO vs. chemotherapy comparisons compared to chemotherapy vs. chemotherapy comparisons (p < 0.001). Exploratory analysis suggested a trend by IO type: for a given change in ORR, 'pure' IO (IO monotherapy and dual-IO) vs. chemotherapy RCTs tended to have a larger OS benefit than IO + chemotherapy vs. chemotherapy RCTs. For ORR vs. PFS, trial-level correlations were strong in the IO-based vs. chemotherapy (R² = 0.84; 0.72-0.95), and chemotherapy vs. chemotherapy strata (R² = 0.69; 0.49-0.88). For OS vs. PFS, correlations were moderate in both strata (R² = 0.49; 0.20-0.78 and R² = 0.49; 0.23-0.76).

CONCLUSION

The larger OS benefit per unit of ORR benefit in IO-based RCTs compared to chemotherapy-only RCTs provides an important addition to the established knowledge regarding the durability and depth of response in IO-based treatments.

Sample size calculation for randomized selection trials with a time-to-event endpoint and a margin of practical equivalence

Selection trials are used to compare potentially active experimental treatments without a control arm. While sample size calculation methods exist for binary endpoints, no such methods are available for time‐to‐event endpoints, even though these are ubiquitous in clinical trials. Recent selection trials have begun using progression‐free survival as their primary endpoint, but have dichotomized it at a specific time point for sample size calculation and analysis. This changes the clinical question and may reduce power to detect a difference between the arms. In this article, we develop the theory for sample size calculation in selection trials where the time‐to‐event endpoint is assumed to follow an exponential or Weilbull distribution. We provide a free web application for sample size calculation, as well as an R package, that researchers can use in the design of their studies.

Association of PD-L1 Expression on Tumor and Immune Cells with Survival in Recurrent or Metastatic Head and Neck Squamous Cell Carcinoma and Assay Validation

Programmed cell death ligand-1 (PD-L1), expressed on both tumor cells (TC) and tumor-associated immune cells (IC), has been shown to be a useful biomarker and predictive of response to anti-PD-L1 agents in certain tumor types. In recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC), there is a growing interest in the role of PD-L1 expression on ICs, as well as TCs, for predicting response to immune checkpoint inhibitors. Using pooled data from the phase II HAWK and CONDOR studies, we investigated the association of baseline PD-L1 expression with durvalumab efficacy in patients with R/M HNSCC. To determine an optimal PD-L1 cut-off point for predicting survival, we assessed PD-L1 expression levels at different TC and IC cut-off points in patients treated with durvalumab. Longer survival was associated with higher TC membrane PD-L1 expression and IC staining. When the combined TC/IC algorithm was applied, a cut-off point for PD-L1 expression of ≥50% on TCs or ≥25% on ICs (TC ≥ 50%/IC ≥ 25%) showed a higher objective response rate (17.2% vs. 8.8%), longer median progression-free survival (2.8 vs. 1.9 months), and longer median overall survival (8.4 vs. 5.4 months) in the PD-L1-high versus PD-L1-low/negative patient populations, respectively. A scoring algorithm combining PD-L1 expression on TCs and ICs using the cut-off point TC ≥ 50%/IC ≥ 25% was optimal for identifying patients with HNSCC most likely to benefit from durvalumab treatment. The new algorithm is robust and can be reproducibly scored by trained pathologists.

SIGNIFICANCE

A novel algorithm for PD-L1 expression using the cut-off point TC ≥ 50%/IC ≥ 25% is robust for identifying patients with HNSCC most likely to benefit from durvalumab treatment and can be reproducibly scored by trained pathologists.

Targeting TRK: A fast-tracked application of precision oncology and future directions

The NTRK genes encode the tropomyosin-related receptor tyrosine kinases TrkA, TrkB and TrkC. TRK receptors regulate the proliferation, differentiation, and survival of many neuronal and non-neuronal glial cells during embryogenesis, thus playing a critical role in synaptic plasticity and the development of nociceptive pathways. Recurrent genomic alterations in NTRK genes, typically fusions involving the 3' region encoding the kinase domain juxtaposed to 5' sequences from numerous partner genes, occur at a low frequency in a wide diversity of adult and pediatric cancers. The contributions of the resulting constitutively activated kinase to oncogenesis and cancer progression are being elucidated. Larotrectinib and entrectinib are potent first-generation TRK inhibitors with IC₅₀ values in the nanomolar range across cancer cell lines harboring NTRK fusions. Larotrectinib is highly selective for TRK receptors, whereas entrectinib also potently inhibits ROS1 and ALK. Clinical trials of both drugs demonstrated significant and durable responses in patients with tumors harboring NTRK alterations, leading to first of its kind cancer agnostic FDA approvals in the United States for drugs targeting a genomic alteration. Unfortunately, acquired resistance inevitably develops. The second-generation TRK inhibitors selitrectinib and repotrectinib are designed to overcome known mechanisms of resistance.

Pre-Treatment Tumor Growth Rate Predicts Clinical Outcomes of Patients With Advanced Non-Small Cell Lung Cancer Undergoing Anti-PD-1/PD-L1 Therapy

Tumor growth rate (TGR; percent size change per month [%/m]) is postulated as an early radio-graphic predictor of response to anti-cancer treatment to overcome limitations of RECIST. We aimed to evaluate the predictive value of pre-treatment TGR (TGR₀) for outcomes of advanced non-small cell lung cancer (aNSCLC) patients treated with anti-PD-1/PD-L1 monotherapy. We retrospectively screened all aNSCLC patients who received PD-1 axis inhibitors in Sun Yat-Sen University Cancer Center between August 2016 and June 2018. TGR₀ was calculated as the percentage change in tumor size per month (%/m) derived from two computed tomography (CT) scans during a "wash-out" period before the initiation of PD-1 axis inhibition. Final follow-up date was August 28, 2019. The X-tile program was used to identify the cut-off value of TGR₀ based on maximum progression-free survival (PFS) stratification. Patients were divided into two groups per the selected TGR₀ cut-off. The primary outcome was the difference of PFS between the two groups. The Kaplan-Meier methods and Cox regression models were performed for survival analysis. A total of 80 eligible patients were included (54 [67.5%] male; median [range] age, 55 [30-74] years). Median (range) TGR₀ was 21.1 (-33.7-246.0)%/m. The optimal cut-off value of TGR₀ was 25.3%/m. Patients with high TGR₀ had shorter median PFS (1.8 months; 95% CI, 1.6 - 2.1 months) than those with low TGR₀ (2.7 months; 95% CI, 0.5 - 4.9 months) (P = 0.005). Multivariate Cox regression analysis revealed that higher TGR₀ independently predicted inferior PFS (hazard ratio [HR] 1.97; 95% CI, 1.08-3.60; P = 0.026). Higher TGR₀ was also significantly associated with less durable clinical benefit rate (34.8% vs. 8.8%, P = 0.007). High pre-treatment TGR was a reliable predictor of inferior PFS and clinical benefit in aNSCLC patients undergoing anti-PD-1/PD-L1 monotherapy. The findings highlight the role of TGR₀ as an early biomarker to predict benefit from immunotherapy and could allow tailoring patient's follow-up.

Endpoint surrogacy in oncology Phase 3 randomised controlled trials

Endpoint surrogacy is an important concept in oncology trials. Using a surrogate endpoint like progression-free survival as the primary endpoint-instead of overall survival-would lead to a potential faster drug approval and therefore more cancer patients with an earlier opportunity to receive the newly approved drugs.

Progression-free survival as a surrogate for overall survival in oncology trials: a methodological systematic review

Background

Progression-free survival (PFS) is a surrogate endpoint widely used for overall survival (OS) in oncology. Validation of PFS as a surrogate must be done for each indication and each intervention. We aimed to identify all studies evaluating the validity of PFS as a surrogate for OS in oncology, and to describe their methodological characteristics.

Methods

We conducted a systematic review by searching MEDLINE via PubMed and the Cochrane Library with no limitation on time, selected relevant studies and extracted data in duplicate on how surrogacy was evaluated (meta-analytic approach, assessment of correlation and level of evaluation).

Results

We identified 91 studies evaluating the validity of PFS as a surrogate for OS in 24 cancer localisations. Although a meta-analytic approach was used in 83 (91%) studies, the methods used to validate PFS as a surrogate of OS were heterogeneous across studies. Of the 47 studies concluding that PFS is a good surrogate for OS, for 15 (32%), there was no quantitative argument for surrogacy.

Conclusions

Although most studies used a meta-analytic approach as recommended, our methodological review highlights heterogeneity in methods and reporting, which stresses the importance of developing and applying clear recommendations in this area.

The Evolution of Clinical Trials in Metastatic Breast Cancer: Design Features and Endpoints That Matter

The evolution of thought in assessing benefit in clinical trials of systemic therapy for metastatic breast cancer (MBC) is well documented, with most agents garnering regulatory approval based either on an advantage in overall survival (OS), time to progression (TTP), or progression-free survival (PFS) over an existing standard of care or objective response rate (ORR). Previous guidance for industry on clinical trial endpoints for the approval of cancer drugs and biologics was provided by the U.S. Food and Drug Administration (FDA) in 2007 and recently updated in 2018. The more recent FDA guidance recognizes that advances in science are facilitating the development of oncology products, which "may also result in the identification of additional endpoints that may be used to support approval of oncology products." This article critically addressed the evolution of thought on the advancement of clinical trials in MBC, from various stakeholder perspectives. Despite the term "stakeholder," the objective of all co-authors and parties concerned is to promote and inform the optimal design, conduct, and reporting of clinical trials for women with advanced breast cancer toward improving and extending lives. This article provides an overview of the evolving perspectives on this issue from the physician, regulatory agency, and patient and/or advocate points of view.