Association between treatment effects on disease progression end points and overall survival in clinical studies of patients with metastatic renal cell carcinoma

LITESPARK-011: belzutifan plus lenvatinib vs cabozantinib in advanced renal cell carcinoma after anti-PD-1/PD-L1 therapy

The first-in-class, small molecule HIF-2α inhibitor, belzutifan, has demonstrated promising antitumor activity in previously treated patients with clear cell renal cell carcinoma (RCC). HIF-2α also regulates VEGF expression and is involved in resistance to anti-VEGF therapy. This study describes the rationale and design for a randomized, phase III study evaluating efficacy and safety of belzutifan plus the tyrosine kinase inhibitor (TKI) lenvatinib versus the TKI cabozantinib in patients with advanced RCC progressing after anti-PD-1/PD-L1 therapy in the first- or second-line setting or as adjuvant therapy. Considering the unmet need for effective and tolerable treatment of advanced RCC following immune checkpoint inhibitors, belzutifan plus lenvatinib may have a positive benefit/risk profile. Clinical Trial Registration: NCT04586231 (ClinicalTrials.gov).

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.

Modelling approaches for histology-independent cancer drugs to inform NICE appraisals: a systematic review and decision-framework

BACKGROUND

The first histology-independent marketing authorisation in Europe was granted in 2019. This was the first time that a cancer treatment was approved based on a common biomarker rather than the location in the body at which the tumour originated. This research aims to explore the implications for National Institute for Health and Care Excellence appraisals.

METHODS

Targeted reviews were undertaken to determine the type of evidence that is likely to be available at the point of marketing authorisation and the analyses required to support National Institute for Health and Care Excellence appraisals. Several challenges were identified concerning the design and conduct of trials for histology-independent products, the greater levels of heterogeneity within the licensed population and the use of surrogate end points. We identified approaches to address these challenges by reviewing key statistical literature that focuses on the design and analysis of histology-independent trials and by undertaking a systematic review to evaluate the use of response end points as surrogate outcomes for survival end points. We developed a decision framework to help to inform approval and research policies for histology-independent products. The framework explored the uncertainties and risks associated with different approval policies, including the role of further data collection, pricing schemes and stratified decision-making.

RESULTS

We found that the potential for heterogeneity in treatment effects, across tumour types or other characteristics, is likely to be a central issue for National Institute for Health and Care Excellence appraisals. Bayesian hierarchical methods may serve as a useful vehicle to assess the level of heterogeneity across tumours and to estimate the pooled treatment effects for each tumour, which can inform whether or not the assumption of homogeneity is reasonable. Our review suggests that response end points may not be reliable surrogates for survival end points. However, a surrogate-based modelling approach, which captures all relevant uncertainty, may be preferable to the use of immature survival data. Several additional sources of heterogeneity were identified as presenting potential challenges to National Institute for Health and Care Excellence appraisal, including the cost of testing, baseline risk, quality of life and routine management costs. We concluded that a range of alternative approaches will be required to address different sources of heterogeneity to support National Institute for Health and Care Excellence appraisals. An exemplar case study was developed to illustrate the nature of the assessments that may be required.

CONCLUSIONS

Adequately designed and analysed basket studies that assess the homogeneity of outcomes and allow borrowing of information across baskets, where appropriate, are recommended. Where there is evidence of heterogeneity in treatment effects and estimates of cost-effectiveness, consideration should be given to optimised recommendations. Routine presentation of the scale of the consequences of heterogeneity and decision uncertainty may provide an important additional approach to the assessments specified in the current National Institute for Health and Care Excellence methods guide.

FURTHER RESEARCH

Further exploration of Bayesian hierarchical methods could help to inform decision-makers on whether or not there is sufficient evidence of homogeneity to support pooled analyses. Further research is also required to determine the appropriate basis for apportioning genomic testing costs where there are multiple targets and to address the challenges of uncontrolled Phase II studies, including the role and use of surrogate end points.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Evidence Synthesis programme and will be published in full in Health Technology Assessment; Vol. 25, No. 76. See the NIHR Journals Library website for further project information.

Surrogate Endpoints in Oncology: Overview of Systematic Reviews and Their Use for Health Decision Making in Mexico

OBJECTIVES

The use of surrogate endpoints (SEs) for cancer drug approval in health systems is common. The objectives of this study were to identify systematic reviews (SRs) that evaluated the correlation of SEs with overall survival (OS) in cancer drugs to analyze the applications of approved cancer drugs with SEs in Mexico and to apply the validation framework proposed by the Institute for Quality and Efficiency in Health Care (IQWiG).

METHODS

An overview of SRs was conducted according to Cochrane Collaboration methodology. Applications for approved cancer drugs with SEs in Mexico were analyzed. The IQWiG validation framework was applied to evaluate the SEs identified in the overview and in the applications in Mexico.

RESULTS

A total of 85 SRs that assessed 192 SEs for different types of cancer were selected. According to the IQWiG model, only 2.5% of the SEs analyzed in the overview and only one of the applications in Mexico could be used as surrogates for OS because the reliability (methodological quality) of the SRs and the strength of the correlation of SEs with OS was mostly low (92%) and low (correlation coefficient r ≤ 0.7; 50.5%), respectively. Of the total number of cancer drugs approved in Mexico, 19.4% used SEs.

CONCLUSIONS

Most SEs for different types of cancer could not be used as surrogates for OS according to the IQWiG model, and their use for the approval of cancer drugs in Mexico is generally not justified.

Association between objective response rate and overall survival in metastatic neuroendocrine tumors treated with radioembolization: a systematic literature review and regression analysis

OBJECTIVES

Neuroendocrine tumors (NETs) are a heterogeneous group of cancers arising from neuroendocrine cells. The aim was to evaluate objective response rate (ORR) as a predictor of overall survival (OS) in patients with metastatic NETs (mNETs) treated with radioembolization (RE).

METHODS

Randomized controlled trials and observational studies of RE treatment of mNETs were identified by systematic literature review (SLR). Pooled ORR and OS estimates were calculated and a weighted generalized linear model (GLM) of ORR as a predictor of OS was derived, stratified by ORR assessment criteria and RE type (Yttrium-90 resin or glass microspheres).

RESULTS

The SLR identified 32 observational studies. Mean ORR was 41% (95% confidence interval 38-45%). The Yttrium-90 resin and glass microsphere GLMs accounted for 59% and 57% of OS deviance, respectively. ORR was a significant predictor of OS in the resin microspheres model (p < 0.001), but not the glass microspheres model (p = 0.11).

CONCLUSIONS

A weighted GLM showed a significant relationship between ORR and OS in patients with mNETs treated with Yttrium-90 resin microspheres. ORR could therefore potentially be an OS surrogate in future trials of Yttrium-90 resin microspheres. Further research is needed to confirm the relationship between ORR and OS and the difference between resin and glass microspheres.

A systematic review of meta-analyses assessing the validity of tumour response endpoints as surrogates for progression-free or overall survival in cancer

BACKGROUND

Tumour response endpoints, such as overall response rate (ORR) and complete response (CR), are increasingly used in cancer trials. However, the validity of response-based surrogates is unclear. This systematic review summarises meta-analyses assessing the association between response-based outcomes and overall survival (OS), progression-free survival (PFS) or time-to-progression (TTP).

METHODS

Five databases were searched to March 2019. Meta-analyses reporting correlation or regression between response-based outcomes and OS, PFS or TTP were summarised.

RESULTS

The systematic review included 63 studies across 20 cancer types, most commonly non-small cell lung cancer (NSCLC), colorectal cancer (CRC) and breast cancer. The strength of association between ORR or CR and either PFS or OS varied widely between and within studies, with no clear pattern by cancer type. The association between ORR and OS appeared weaker and more variable than that between ORR and PFS, both for associations between absolute endpoints and associations between treatment effects.

CONCLUSIONS

This systematic review suggests that response-based endpoints, such as ORR and CR, may not be reliable surrogates for PFS or OS. Where it is necessary to use tumour response to predict treatment effects on survival outcomes, it is important to fully reflect all statistical uncertainty in the surrogate relationship.

CHALLENGES AND METHODOLOGIES IN USING PROGRESSION FREE SURVIVAL AS A SURROGATE FOR OVERALL SURVIVAL IN ONCOLOGY

OBJECTIVES

A primary outcome in oncology trials is overall survival (OS). However, to estimate OS accurately requires a sufficient number of patients to have died, which may take a long time. If an alternative end point is sufficiently highly correlated with OS, it can be used as a surrogate. Progression-free survival (PFS) is the surrogate most often used in oncology, but does not always satisfy the correlation conditions for surrogacy. We analyze the methodologies used when extrapolating from PFS to OS.

METHODS

Davis et al. previously reviewed the use of surrogate end points in oncology, using papers published between 2001 and 2011. We extend this, reviewing papers published between 2012 and 2016. We also examine the reporting of statistical methods to assess the strength of surrogacy.

RESULTS

The findings from 2012 to 2016 do not differ substantially from those of 2001 to 2011: the same factors are shown to affect the relationship between PFS and OS. The proportion of papers reporting individual patient data (IPD), strongly recommended for full assessment of surrogacy, remains low: 33 percent. A wide range of methods has been used to determine the appropriateness of surrogates. While usually adhering to reporting standards, the standard of scholarship appears sometimes to be questionable and the reporting of results often haphazard.

CONCLUSIONS

Standards of analysis and reporting PFS to OS surrogate studies should be improved by increasing the rigor of statistical reporting and by agreeing to a minimum set of reporting guidelines. Moreover, the use of IPD to assess surrogacy should increase.

Cabozantinib versus sunitinib as initial therapy for metastatic renal cell carcinoma of intermediate or poor risk (Alliance A031203 CABOSUN randomised trial): Progression-free survival by independent review and overall survival update

BACKGROUND

The randomised phase 2 CABOSUN trial comparing cabozantinib with sunitinib as initial therapy for advanced renal cell carcinoma (RCC) of intermediate or poor risk met the primary end-point of improving progression-free survival (PFS) as assessed by investigator. We report PFS by independent radiology review committee (IRC) assessment, ORR per IRC and updated overall survival (OS).

PATIENTS AND METHODS

Previously untreated patients with advanced RCC of intermediate or poor risk by IMDC criteria were randomised 1:1 to cabozantinib 60 mg daily or sunitinib 50 mg daily (4 weeks on/2 weeks off). Stratification was by risk group and presence of bone metastases.

RESULTS

A total of 157 patients were randomised 1:1 to cabozantinib (n = 79) or sunitinib (n = 78). Median PFS per IRC was 8.6 months (95% confidence interval [CI] 6.8-14.0) versus 5.3 months (95% CI 3.0-8.2) for cabozantinib versus sunitinib (hazard ratio [HR] 0.48 [95% CI 0.31-0.74]; two-sided p = 0.0008), and ORR per IRC was 20% (95% CI 12.0-30.8) versus 9% (95% CI 3.7-17.6), respectively. Subgroup analyses of PFS by stratification factors and MET tumour expression were consistent with results for the overall population. With a median follow-up of 34.5 months, median OS was 26.6 months (95% CI 14.6-not estimable) with cabozantinib and 21.2 months (95% CI 16.3-27.4) with sunitinib (HR 0.80 [95% CI 0.53-1.21]. The incidence of grade 3 or 4 adverse events was 68% for cabozantinib and 65% for sunitinib.

CONCLUSIONS

In this phase 2 trial, cabozantinib treatment significantly prolonged PFS per IRC compared with sunitinib as initial systemic therapy for advanced RCC of poor or intermediate risk.

TRIAL REGISTRATION NUMBER

NCT01835158.

An individualized prognostic signature and multi‑omics distinction for early stage hepatocellular carcinoma patients with surgical resection

Previously reported prognostic signatures for predicting the prognoses of postsurgical hepatocellular carcinoma (HCC) patients are commonly based on predefined risk scores, which are hardly applicable to samples measured by different laboratories. To solve this problem, using gene expression profiles of 170 stage I/II HCC samples, we identified a prognostic signature consisting of 20 gene pairs whose within-sample relative expression orderings (REOs) could robustly predict the disease-free survival and overall survival of HCC patients. This REOs-based prognostic signature was validated in two independent datasets. Functional enrichment analysis showed that the patients with high-risk of recurrence were characterized by the activations of pathways related to cell proliferation and tumor microenvironment, whereas the low-risk patients were characterized by the activations of various metabolism pathways. We further investigated the distinct epigenomic and genomic characteristics of the two prognostic groups using The Cancer Genome Atlas samples with multi-omics data. Epigenetic analysis showed that the transcriptional differences between the two prognostic groups were significantly concordant with DNA methylation alternations. The signaling network analysis identified several key genes (e.g. TP53, MYC) with epigenomic or genomic alternations driving poor prognoses of HCC patients. These results help us understand the multi-omics mechanisms determining the outcomes of HCC patients.

Do Surrogate Endpoints Better Correlate with Overall Survival in Studies That Did Not Allow for Crossover or Reported Balanced Postprogression Treatments? An Application in Advanced Non-Small Cell Lung Cancer

BACKGROUND

In previous studies, correlation between overall survival (OS) and surrogate endpoints like objective response rate (ORR) or progression-free survival (PFS) in advanced non-small cell lung cancer (NSCLC) was poor. This can be biased by crossover and postprogression treatments.

OBJECTIVES

To evaluate the relationship between these two surrogate endpoints and OS in advanced NSCLC studies that did not allow for crossover or reported balanced post-progression treatments.

METHODS

A systematic review in patients with advanced NSCLC receiving second- and further-line therapy was performed. The relationship between the absolute difference in ORR or median PFS (mPFS) and the absolute difference in median OS (mOS) was assessed using the correlation coefficient (R) and weighted regression models. The analysis was repeated in predefined data cuts based on crossover and balance of postprogression treatments. When the upper limit of R's 95% confidence interval (CI) was more than 0.7, the surrogate threshold effect (STE) was estimated.

RESULTS

In total, 146 randomized clinical trials (43,061 patients) were included. The mean ORR, mPFS, and mOS were 12.2% ± 11.2%, 3.2 ± 1.3 months, and 9.6 ± 4.1 months, respectively. The correlation coefficients of ORR and mPFS were 0.181 (95% CI 0.016-0.337) and 0.254 (95% CI 0.074-0.418), respectively, with mOS. Nevertheless, in trials that did not allow crossover and reported balanced postprogression treatments, the correlation coefficients of ORR and mPFS were 0.528 (95% CI 0.081-0.798) and 0.778 (95% CI 0.475-0.916), respectively, with mOS. On the basis of STE estimation, in trials showing significant treatment effect size of 41.0% or more ORR or 4.15 or more mPFS months, OS benefit can be expected with sufficient certainty.

CONCLUSIONS

Crossover and postprogression treatments may bias the relationship between surrogate endpoints and OS. Presented STE calculation can be used to interpret treatment effect on either ORR or PFS when used as primary endpoints.

Evaluation of disease-free survival as an intermediate metric of overall survival in patients with localized renal cell carcinoma: A trial-level meta-analysis

BACKGROUND

Overall survival (OS) is a critical endpoint in adjuvant trials but requires long durations to events and significant patient resources. In the current study, the authors assessed whether disease-free survival (DFS) can be an early clinical surrogate for OS in the adjuvant setting for localized renal cell carcinoma (RCC).

METHODS

Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, the authors performed a systematic literature review of PubMed and the American Society of Clinical Oncology, European Society for Medical Oncology, and ClinicalTrial.gov Web sites (1996-2016). Inclusion in the current study required randomized controlled trials (RCTs) of adjuvant systemic therapy for localized RCC after nephrectomy with ≥3 years of outcomes data. Data regarding hazard ratios (HRs) and 5-year event-free rates from Kaplan-Meier estimates were extracted. A trial-level meta-analysis correlated estimates of 5-year DFS and 5-year OS as well as treatment effects (HRs) on these endpoints, weighted by the number of DFS events. R-squared ≥ 0.7 was prespecified as being indicative of a strong correlation and the potential for surrogacy.

RESULTS

Thirteen RCTs encompassing 6473 patients who were treated with a variety of systemic therapies met eligibility. Only a modest correlation was observed between 5-year DFS and 5-year OS rates (R-squared, 0.48; 95% confidence interval, 0.14-0.67) and between treatment effects as measured by DFS and OS HRs (R-squared, 0.44; 95% confidence interval, 0.00-0.69).

CONCLUSIONS

Across RCTs of adjuvant systemic therapy for localized RCC, there was no strong correlation noted between 5-year DFS and 5-year OS rates or between treatment effects on these endpoints. These results highlight the need to identify alternative and more rapid clinical or biologic endpoints to hasten drug development and improve clinical outcomes. Cancer 2018;124:925-33. © 2017 American Cancer Society.

Progression-free survival as a surrogate endpoint in advanced neuroendocrine neoplasms

In oncology clinical trials, overall survival (OS) is considered the gold standard outcome measure. In phase III trials for neuroendocrine neoplasms (NENs), however, progression-free survival (PFS) is more frequently used, as NENs are relatively rare and indolent neoplasms. But this surrogacy of PFS for OS has never been systematically validated. We, therefore, performed a literature-based analysis of phase II and III trials for NENs to evaluate the correlation between PFS and OS in NENs treated with medical treatment. We identified phase II and III clinical trials of medical treatment for advanced NENs based on a systematic electronic search using MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials. A total of 20 trials were identified, and 2530 patients and 30 treatment arms were included in the analysis. There was a statistically significant relationship between PFS and OS (r_s , 0.587; 95% confidence interval, 0.249-0.925). Conversely, the objective response rate was not significantly correlated with OS. The results of subgroup analyses indicated that the correlation between PFS and OS was higher for study arms that prohibited concomitant therapy with somatostatin analogues than for those that permitted it. The results of the present analysis indicate that PFS is significantly correlated with OS, and suggest that PFS is an acceptable surrogate for OS in clinical trials for NENs.

Treatment of Advanced Hepatocellular Carcinoma after Failure of Sorafenib Treatment: Subsequent or Additional Treatment Interventions Contribute to Prolonged Survival Postprogression

Background

Sorafenib is a first-line treatment option for advanced hepatocellular carcinoma (HCC) patients; however, survival predictors upon progression have not been well characterized. In the present study, we aimed to show the efficacy of multidisciplinary therapy for patients who had failed to respond to sorafenib treatment.

Methods

Among 146 BCLC stage B or C HCC patients treated with sorafenib monotherapy between July 2009 and August 2014, the first radiological progression according to the modified RECIST was identified in 71 patients; factors predicting overall survival (OS) and survival postprogression (SPP) were analyzed in these patients.

Results

The median OS and SPP for patients who failed to respond to sorafenib treatment were 10.5 and 6.2 months, respectively, and the SPP was strongly correlated with the OS (r = 0.982, P < 0.01, and R² = 0.965). The independent predictors of OS and SPP were identical. The predictors of SPP were des-gamma-carboxy prothrombin, progression of portal vein thrombosis, and subsequent second-line or additional treatment.

Conclusions

SPP is closely associated with OS and might be notable in patients who have failed to respond to initial sorafenib treatment. Furthermore, interventions consisting of other treatment options upon the appearance of progression might prolong OS.

Primary Tumor Characteristics Are Important Prognostic Factors for Sorafenib-Treated Patients with Metastatic Renal Cell Carcinoma: A Retrospective Multicenter Study

We aimed to identify prognostic factors associated with progression-free survival (PFS) and overall survival (OS) in metastatic renal cell carcinoma (mRCC) patients treated with sorafenib. We investigated 177 patients, including 116 who received sorafenib as first-line therapy, using the Cox regression model. During a median follow-up period of 19.2 months, the PFS and OS were 6.4 and 32.6 months among all patients and 7.4 months and undetermined for first-line sorafenib-treated patients, respectively. Clinical T3-4 stage (hazard ratio [HR] 2.56) and a primary tumor size >7 cm (HR 0.34) were significant prognostic factors for PFS among all patients, as were tumor size >7 cm (HR 0.12), collecting system invasion (HR 5.67), and tumor necrosis (HR 4.11) for OS (p < 0.05). In first-line sorafenib-treated patients, ≥4 metastatic lesions (HR 28.57), clinical T3-4 stage (HR 4.34), collecting system invasion (univariate analysis HR 2.11; multivariate analysis HR 0.07), lymphovascular invasion (HR 13.35), and tumor necrosis (HR 6.69) were significant prognosticators of PFS, as were bone metastasis (HR 5.49) and clinical T3-4 stages (HR 4.1) for OS (p < 0.05). Our study thus identified a number of primary tumor-related characteristics as important prognostic factors in sorafenib-treated mRCC patients.

The effect of information on preferences for treatments of metastatic renal cell carcinoma

OBJECTIVE

Limited information exists regarding the effect of uncertainty in outcomes on patient preferences for metastatic renal cell carcinoma (mRCC) treatments. This study tested the effect on patients' preferences and willingness to tolerate toxicities when patients were provided with information about possible correlations between treatment-related toxicities and efficacy.

RESEARCH DESIGN AND METHODS

Patients with self-reported RCC diagnosis completed an online survey. Respondents were randomly assigned to the information treatment (i.e. information about the possible correlation). Medicines were defined by progression-free survival (PFS), three toxicities potentially correlated with PFS, and one toxicity uncorrelated with PFS. Direct-elicitation questions measured willingness to tolerate the toxicities, preferences for medicines with higher toxicity but a higher chance of longer PFS, and preferences for medicines with higher toxicity during treatment and a 2 week dosing schedule break. A discrete-choice experiment (DCE) tested the effect of information on relative preferences for medication attributes.

RESULTS

A total of 378 RCC patients completed the survey. Respondents who received the information reported greater willingness to accept more severe toxicities and preferred treatment with a higher chance of longer PFS but more severe toxicities. The DCE results were consistent with the hypothesis that the information increased willingness to tolerate toxicities; however, the results were only statistically significant for changes in fatigue (none to severe; p < 0.05) and hypertension (none to manageable; p < 0.05).

LIMITATIONS

Online recruitment through patient support groups may limit generalizability to the population of patients with mRCC who would be candidates for the targeted therapies.

CONCLUSIONS

The findings suggest that RCC patients have diverse preferences but may be willing to continue targeted therapies, even in the presence of severe toxicities, if there is a chance of improved clinical benefit. Physicians should provide patients with comprehensive information about medication features, including toxicities and efficacy (and their potential correlation), to improve compliance and optimize outcomes.

Validation of surrogate endpoints in advanced solid tumors: systematic review of statistical methods, results, and implications for policy makers

OBJECTIVES

Licensing of, and coverage decisions on, new therapies should rely on evidence from patient-relevant endpoints such as overall survival (OS). Nevertheless, evidence from surrogate endpoints may also be useful, as it may not only expedite the regulatory approval of new therapies but also inform coverage decisions. It is, therefore, essential that candidate surrogate endpoints be properly validated. However, there is no consensus on statistical methods for such validation and on how the evidence thus derived should be applied by policy makers.

METHODS

We review current statistical approaches to surrogate-endpoint validation based on meta-analysis in various advanced-tumor settings. We assessed the suitability of two surrogates (progression-free survival [PFS] and time-to-progression [TTP]) using three current validation frameworks: Elston and Taylor's framework, the German Institute of Quality and Efficiency in Health Care's (IQWiG) framework and the Biomarker-Surrogacy Evaluation Schema (BSES3).

RESULTS

A wide variety of statistical methods have been used to assess surrogacy. The strength of the association between the two surrogates and OS was generally low. The level of evidence (observation-level versus treatment-level) available varied considerably by cancer type, by evaluation tools and was not always consistent even within one specific cancer type.

CONCLUSIONS

Not in all solid tumors the treatment-level association between PFS or TTP and OS has been investigated. According to IQWiG's framework, only PFS achieved acceptable evidence of surrogacy in metastatic colorectal and ovarian cancer treated with cytotoxic agents. Our study emphasizes the challenges of surrogate-endpoint validation and the importance of building consensus on the development of evaluation frameworks.

Strength of Validation for Surrogate End Points Used in the US Food and Drug Administration's Approval of Oncology Drugs

OBJECTIVE

To determine the strength of the surrogate-survival correlation for cancer drug approvals based on a surrogate.

PARTICIPANTS AND METHODS

We performed a retrospective study of the US Food and Drug Administration (FDA) database, with focused searches of MEDLINE and Google Scholar. Among cancer drugs approved based on a surrogate end point, we examined previous publications assessing the strength of the surrogate-survival correlation. Specifically, we identified the percentage of surrogate approvals lacking any formal analysis of the strength of the surrogate-survival correlation, and when conducted, the strength of such correlations.

RESULTS

Between January 1, 2009, and December 31, 2014, the FDA approved marketing applications for 55 indications based on a surrogate, of which 25 were accelerated approvals and 30 were traditional approvals. We could not find any formal analyses of the strength of the surrogate-survival correlation in 14 out of 25 accelerated approvals (56%) and 11 out of 30 traditional approvals (37%). For accelerated approvals, just 4 approvals (16%) were made where a level 1 analysis (the most robust way to validate a surrogate) had been performed, with all 4 studies reporting low correlation (r≤0.7). For traditional approvals, a level 1 analysis had been performed for 15 approvals (50%): 8 (53%) reported low correlation (r≤0.7), 4 (27%) medium correlation (r>0.7 to r<0.85), and 3 (20%) high correlation (r≥0.85) with survival.

CONCLUSIONS

The use of surrogate end points for drug approval often lacks formal empirical verification of the strength of the surrogate-survival association.

Lifetime cost of everolimus vs axitinib in patients with advanced renal cell carcinoma who failed prior sunitinib therapy in the US

OBJECTIVE

Everolimus and axitinib are approved in the US to treat patients with advanced renal cell carcinoma (RCC) after failure on sunitinib or sorafenib, and one prior systemic therapy (e.g., sunitinib), respectively. Two indirect comparisons performed to evaluate progression-free survival in patients treated with everolimus vs axitinib suggested similar efficacy between the two treatments. Therefore, this analysis compares the lifetime costs of these two therapies among sunitinib-refractory advanced RCC patients from a US payer perspective.

RESEARCH DESIGN AND METHODS

A Markov model was developed to simulate a cohort of sunitinib-refractory advanced RCC patients and estimate the cost of treating patients with everolimus vs axitinib. The following health states were included: stable disease without adverse events (AEs), stable disease with AEs, disease progression (PD), and death. The model included the following resources: active treatments, post-progression treatments, adverse events, physician and nurse visits, scans and tests, and palliative care. Resource utilization inputs were derived from a US claims database analysis. Additionally, a 3% annual discount rate was applied to costs, and the robustness of the model results was tested by conducting sensitivity analyses, including those on dosing scheme and post-progression treatment costs.

RESULTS

Base case results demonstrated that patients treated with everolimus cost an average of $12,985 (11%) less over their lifetimes than patients treated with axitinib. The primary difference in costs was related to active treatment, which was largely driven by axitinib's higher dose intensity. RESULTS remained consistent across sensitivity analyses for AE and PD treatment costs, as well as dose intensity and discount rates.

CONCLUSION

The results suggest that everolimus likely leads to lower lifetime costs than axitinib for sunitinib-refractory advanced RCC patients in the US.

Interpreting overall survival results when progression-free survival benefits exist in today's oncology landscape: a metastatic renal cell carcinoma case study

Background

The debate surrounding the acceptance of progression-free survival (PFS) as an intermediate endpoint to overall survival (OS) has grown in recent years, due to the challenges in demonstrating an OS benefit within clinical trials today. PFS is generally a good predictor of OS for cases where survival post-progression (SPP) is short, and less so when SPP is long. SPP depends on multiple factors, including residual effect from experimental treatment and effect from crossover or other subsequent therapies, posing unique challenges into the translation of PFS benefit into OS.

Methods

The objective of this analysis was to conduct simulations investigating how increasing SPP impacts PFS translation to OS, utilizing data from the AXIS (axitinib versus sorafenib in advanced metastatic renal cell carcinoma) trial. The underlying assumption was a treatment benefit in PFS (the PFS distribution parameters were chosen to be equal to median PFS in the AXIS trial) but no treatment effect on SPP, implying that PFS improvement is directly reflected in OS improvement.

Results

The probability of a statistically significant difference between arms for OS decreased from 54.7% to 6.1% when median SPP was increased from one to 20 months. The probability of the hazard ratio of OS being ≥0.9 was similarly increased from 24.3% to 72.6%, even though the hazard ratio for PFS was 0.69.

Conclusion

The present study shows that when simulated SPP is added to trial PFS data, the existing PFS benefit is diluted. Knowing that the AXIS treatment arms are well balanced with respect to post-trial treatments, we conclude that the PFS to OS benefit translation is primarily obscured by random variability largely unrelated to the true outcomes. The implications for drug development are not insignificant, as there would be a need to include more patients in studies or utilize a longer follow-up time to overcome the SPP variability issue.

Assessment of progression-free survival as a surrogate end-point for overall survival in patients with metastatic renal cell carcinoma

BACKGROUND

To determine suitability of progression-free survival (PFS) as a surrogate end-point for overall survival (OS), we evaluated the relationship between PFS and OS in 750 treatment-naïve metastatic renal cell carcinoma (mRCC) patients who received sunitinib or interferon-alpha (IFN-α) in a phase III study.

METHODS

The relationship between PFS and post-progression survival (PPS; the difference between PFS and OS) was studied, which correctly removes inherent dependencies between PFS and OS, to properly estimate whether and to what extent PFS can serve as a surrogate for OS. A Weibull parametric model to failure time data was fit to determine whether longer PFS was significantly and meaningfully predictive of longer PPS. In a sensitivity analysis by Kaplan-Meier non-parametric method, PPS curves for three approximately equal numbered groups of patients categorised by PFS were compared by log-rank test.

RESULTS

In the Weibull parametric model, longer PFS was significantly predictive of longer PPS (P<0.001). The model also allowed prediction of estimated median PPS duration from actual PFS times. In the Kaplan-Meier (non-parametric) analysis, incrementally longer PFS was also associated with longer PPS, and the PPS curves for the three PFS groups were significantly different (P<0.0001).

CONCLUSIONS

A positive relationship was found between PFS and PPS duration in individual mRCC patients randomised to first-line treatment with sunitinib or IFN-α. These results indicate that PFS can act as a surrogate end-point for OS in the first-line mRCC setting and provide clinical researchers with a potentially useful approach to estimate median PPS based on PFS.

Surrogate end points and postprogression survival in renal cell carcinoma: an analysis of first-line trials with targeted therapies

Our end point was to determine the correlations between progression-free survival (PFS), postprogression survival (PPS), response rate (RR), and disease control rate (DCR) (RR + stable disease) and overall survival (OS) in first-line trials of renal cell carcinoma (RCC) treated with targeted therapies and to identify a potential surrogate for OS. Data were collected from first-line phase III randomized trials in RCC. Linear regression was undertaken to evaluate the correlations between end points and a potential surrogate end point for OS. Six randomized trials were identified containing a total of 7 treatment arms. The nonparametric Spearman rank correlation coefficients (r(s)) between PFS, PPS, and RR/DCR and OS are 0.869, and 1, 0.96/1 (all P < .0001), respectively. There is a strong relationship between differences (Δ) in DCR and ΔOS (r(s) = 1). The slope of the regression line is 0.3963 ± 0.0019, indicating that a novel drug producing a 10% increase for DCR will yield an estimated absolute 3.9% increase in OS. In first-line trials including novel targeted agents for RCC, PFS is a relatively flawed surrogate end point because of PPS influence. Improvement in DCR is strongly associated with improvement in median OS. In this population, DCR may be an appropriate surrogate for OS.