Alternatives to the Kaplan-Meier estimator of progression-free survival.

Progression-free survival (PFS), defined as the time from randomization to progression of disease or death, has been indicated as an endpoint to support accelerated approval of certain cancer drugs by the U.S. FDA. The standard Kaplan-Meier (KM) estimator of PFS, however, can result in significantly biased estimates. A major source for the bias results from the substitution of censored progression times with death times. Currently, to ameliorate this bias, several sensitivity analyses based on rather arbitrary definitions of PFS censoring are usually conducted. In addition, especially in the advanced cancer setting, patients with censored progression and observed death times have the potential to experience disease progression between those two times, in which case their true PFS time is actually between those times. In this paper, we present two alternative nonparametric estimators of PFS, which statistically incorporate survival data often available for those patients who are censored with respect to progression to obtain less biased estimates. Through extensive simulations, we show that these estimators greatly reduce the bias of the standard KM estimator and can also be utilized as alternative sensitivity analyses with a solid statistical basis in lieu of the arbitrarily defined analyses currently used. An example is also given using an ECOG-ACRIN Cancer Research Group advanced breast cancer study.

Efficacy of simtuzumab versus placebo in patients with idiopathic pulmonary fibrosis: a randomised, double-blind, controlled, phase 2 trial.

BACKGROUND: Lysyl oxidase-like 2 (LOXL2) catalyses collagen cross-linking and is implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF). The aim of this study was to investigate the efficacy and safety of simtuzumab, a monoclonal antibody against LOXL2, in patients with IPF. METHODS: In this randomised, double-blind, phase 2 trial, we recruited patients aged 45-85 years with definite IPF diagnosed prior to 3 years of screening from 183 hospitals and respiratory clinics in 14 countries. Eligible patients, stratified by baseline forced vital capacity (FVC), serum LOXL2 (sLOXL2) concentrations, and pirfenidone and nintedanib use, were randomly assigned (1:1) to inject 125 mg/mL simtuzumab or placebo subcutaneously once a week. The primary endpoints were progression-free survival, defined as time to all-cause death or a categorical decrease from baseline in FVC % predicted, in the intention-to-treat population, in patients with sLOXL2 concentrations in the 50th percentile or higher, and in patients with sLOXL2 concentrations in the 75th percentile or higher. Treatment duration was event-driven, and interim analyses were planned and conducted after approximately 120 and 200 progression-free survival events, respectively, occurred. We compared treatment groups with the stratified log-rank test. This study is registered with ClinicalTrials.gov, number NCT01769196. FINDINGS: Patients with IPF were recruited between Jan 31, 2013, and June 1, 2015. The intention-to-treat population included 544 randomly assigned patients (272 patients in both groups), and the safety population included 543 randomly assigned patients who received at least one dose of study medication. The study was terminated when the second interim analysis met the prespecified futility stopping criteria in the intention-to-treat population. We noted no difference in progression-free survival between simtuzumab and placebo in the intention-to-treat population (median progression free survival times of 12·6 months and 15·4 months for simtuzumab and placebo, respectively; stratified HR 1·13, 95% CI 0·88-1·45; p=0·329) and in patients with baseline sLOXL2 in the 50th percentile or higher (median progression-free survival 11·7 months and 14·3 months for simtuzumab and placebo, respectively; stratified HR 1·03, 95% CI 0·74-1·43; p=0·851), or in the 75th percentile or higher (median progression-free survival 11·6 months and 16·9 months for simtuzumab and placebo, respectively; stratified HR 1·20, 95% CI 0·72-2·00; p=0·475). The incidence of adverse events and serious adverse events was similar between treatment groups. The most common adverse events in both the simtuzumab and placebo groups were dyspnoea, cough, upper respiratory tract infection, and worsening of IPF; and the most common grade 3 or 4 adverse events were worsening of IPF, dyspnoea, and pneumonia. INTERPRETATION: Simtuzumab did not improve progression-free survival in a well-defined population of patients with IPF. Our data do not support the use of simtuzumab for patients with IPF. FUNDING: Gilead Sciences Inc.

Design of a phase 2 clinical trial of an ASK1 inhibitor, GS-4997, in patients with diabetic kidney disease.

BACKGROUND: Most patients with diabetic kidney disease (DKD) experience disease progression despite receiving standard care therapy. Oxidative stress is associated with DKD severity and risk of progression, but currently approved therapies do not directly attenuate the pathologic consequences of oxidative stress. GS-4997 is a once daily, oral molecule that inhibits Apoptosis Signal-regulating Kinase 1 (ASK1), which is a key mediator of the deleterious effects of oxidative stress. METHODS: We describe the rationale and design of a Phase 2 placebo-controlled clinical trial investigating the effects of GS-4997 in patients with T2DM and stage 3/4 DKD receiving standard of care therapy. Approximately, 300 subjects will be randomized in a stratified manner, based on the estimated glomerular filtration rate (eGFR) and urine albumin to creatinine ratio, to one of four arms in this dose-ranging study. The primary endpoint is change in eGFR at 48 weeks, and the key secondary endpoint is change in albuminuria. CONCLUSION: Guided by the biology of oxidative stress signaling through ASK1, the biology of DKD pathogenesis, and solid statistical methods, the decisions made for this Phase 2 study regarding delineating study population, efficacy outcomes, treatment period and statistical methods represent innovative attempts to resolve challenges specific to DKD study design.

Joint probability of statistical success of multiple phase III trials.

In drug development, after completion of phase II proof-of-concept trials, the sponsor needs to make a go/no-go decision to start expensive phase III trials. The probability of statistical success (PoSS) of the phase III trials based on data from earlier studies is an important factor in that decision-making process. Instead of statistical power, the predictive power of a phase III trial, which takes into account the uncertainty in the estimation of treatment effect from earlier studies, has been proposed to evaluate the PoSS of a single trial. However, regulatory authorities generally require statistical significance in two (or more) trials for marketing licensure. We show that the predictive statistics of two future trials are statistically correlated through use of the common observed data from earlier studies. Thus, the joint predictive power should not be evaluated as a simplistic product of the predictive powers of the individual trials. We develop the relevant formulae for the appropriate evaluation of the joint predictive power and provide numerical examples. Our methodology is further extended to the more complex phase III development scenario comprising more than two (K > 2) trials, that is, the evaluation of the PoSS of at least k0 (k0≤ K) trials from a program of K total trials.

Evaluating and adjusting for premature censoring of progression-free survival.

The intent-to-treat principle, grouping subjects as they were randomized and following all subjects to the endpoint or the end of study, allows valid statistical comparisons. Progression-free survival (PFS) has been used as a decision-making endpoint in oncology. It can be difficult to have a meaningful intent-to-treat analysis of PFS as some studies have extensive loss to follow-up for PFS. In the analysis, subjects lost to follow-up for PFS have their PFS times censored, with the censoring treated as noninformative. We use remaining overall survival to investigate whether premature censoring for PFS is informative and the potential bias in treating such censoring as noninformative.

Assessment of audit methodologies for bias evaluation of tumor progression in oncology clinical trials.

As progression-free survival (PFS) has become increasingly used as the primary endpoint in oncology phase III trials, the U.S. Food and Drug Administration (FDA) has generally required a complete-case blinded independent central review (BICR) of PFS to assess and reduce potential bias in the investigator or local site evaluation. However, recent publications and FDA analyses have shown a high correlation between local site evaluation and BICR assessments of the PFS treatment effect, which questions whether complete-case BICR is necessary. One potential alternative is to use BICR as an audit tool to detect evaluation bias in the local site evaluation. In this article, the performance characteristics of two audit methods proposed in the literature are evaluated on 26 prospective, randomized phase III registration trials in nonhematologic malignancies. The results support that a BICR audit to assess potential bias in the local site evaluation is a feasible approach. However, implementation and logistical challenges need further consideration and discussion.

Evaluation of Blinded Independent Central Review of Tumor Progression in Oncology Clinical Trials: A Meta-analysis.

Use of blinded independent central review (BICR) has become more common in oncology phase 3 trials as progression-free survival (PFS) has been increasingly used as an endpoint for regulatory approval. Since PFS is primarily a radiographic endpoint, BICR has been implemented to assess and reduce potential bias in the local evaluation (LE) of PFS. Recent publications note an agreement between LE and BICR of the ultimate reported PFS treatment effect, which questions the need for costly and time-consuming complete-case BICR of PFS. A meta-analysis was conducted to systematically evaluate the relationship between BICR- and LE-assessed PFS based on FDA's regulatory experience from 2005 to present. Our results support the claim that a complete review of all radiographs by BICR may not be necessary for oncology trials, and alternative methods should be explored to evaluate bias. One potential alternative is to use BICR as an audit tool to detect evaluation bias in LE assessments.

L-carnitine supplementation for the management of fatigue in patients with cancer: an eastern cooperative oncology group phase III, randomized, double-blind, placebo-controlled trial.

PURPOSE: L-carnitine, a popular complementary and alternative medicine product, is used by patients with cancer for the treatment of fatigue, the most commonly reported symptom in this patient population. The purpose of this study was to determine the efficacy of L-carnitine supplementation as a treatment for fatigue in patients with cancer. PATIENTS AND METHODS: In this double-blind, placebo-controlled trial, patients with invasive malignancies and fatigue were randomly assigned to either 2 g/d of L-carnitine oral supplementation or matching placebo. The primary end point was the change in average daily fatigue from baseline to week 4 using the Brief Fatigue Inventory (BFI). RESULTS: Three hundred seventy-six patients were randomly assigned to treatment with L-carnitine supplementation or placebo. L-carnitine supplementation resulted in significant carnitine plasma level increase by week 4. The primary outcome, fatigue, measured using the BFI, improved in both arms compared with baseline (L-carnitine: -0.96, 95% CI, -1.32 to -0.60; placebo: -1.11, 95% CI -1.44 to -0.78). There were no statistically significant differences between arms (P = .57). Secondary outcomes, including fatigue measured by the Functional Assessment of Chronic Illness Therapy-Fatigue instrument, depression, and pain, did not show significant difference between arms. A separate analysis of patients who were carnitine-deficient at baseline did not show statistically significant improvement in fatigue or other outcomes after L-carnitine supplementation. CONCLUSION: Four weeks of 2 g of L-carnitine supplementation did not improve fatigue in patients with invasive malignancies and good performance status.

FDA approval summary: sunitinib for the treatment of progressive well-differentiated locally advanced or metastatic pancreatic neuroendocrine tumors.

On May 20, 2011, the U.S. Food and Drug Administration (FDA) approved sunitinib malate capsules (Sutent®; Pfizer, Inc., New York) for the treatment of progressive, well-differentiated pancreatic neuroendocrine tumors (pNETs) in patients with unresectable locally advanced or metastatic disease. In a phase III randomized trial, 171 patients received either sunitinib (37.5 mg) or placebo once daily. The progression-free survival (PFS) interval was the primary efficacy endpoint. Secondary endpoints included the overall survival (OS) time, objective response rate (ORR), patient-reported outcomes, and safety. Based on early results favoring sunitinib, the independent data monitoring committee recommended trial termination prior to the prespecified interim analysis. This premature analysis may have led to an overestimate of the treatment effect. In the FDA analysis of investigator-assessed PFS times, the median values for the sunitinib and placebo arms were 10.2 months and 5.4 months, respectively. The ORRs were 9.3% and 0% in the sunitinib and placebo arms, respectively. The OS data were not mature at the time of approval and were confounded by 69% crossover. Common adverse reactions in patients receiving sunitinib included diarrhea, nausea, asthenia, fatigue, neutropenia, hypertension, and palmar-plantar erythrodysesthesia syndrome. Two patients on sunitinib died as a result of cardiac failure. The Oncologic Drugs Advisory Committee voted eight to two that, despite residual uncertainty about the magnitude of the PFS effect because of early trial termination, sunitinib demonstrated a favorable benefit-risk profile in pNET patients. The FDA concurred with the committee's assessment and granted sunitinib regular approval for this rare malignancy with few available therapies.

Overestimation of the effect size in group sequential trials.

Group sequential designs (GSD), which provide for interim monitoring of efficacy data and allow potential early trial termination while preserving the type I error rate, have become commonplace in oncology clinical trials. Although ethically appealing, GSDs tend to overestimate the true treatment effect size at early interim analyses. Overestimation of the treatment effect may exaggerate the benefit of a drug and provide imprecise information for physicians and their patients about a drug's true effect. The cause and effect of such a phenomenon are generally not well understood by many in clinical trial practice. In this article, we provide a graphical explanation for why the phenomenon of overestimation in GSDs occurs. The potential overestimation of the magnitude of the treatment effect is of particular concern in oncology, in which the more subjective endpoint of progression-free survival has increasingly been adopted as the primary endpoint in pivotal phase III trials.

Testing in a Prespecified Subgroup and the Intent-to-Treat Population.

In many settings, testing has been proposed to assess the effect of an experimental regimen within a biomarker-positive subgroup where it is biologically plausible that benefit is stronger in such patients, and in the overall population that also includes biomarker-negative subjects less likely to benefit from that regimen. A statistically favorable result in the biomarker-positive subgroup would lead to a claim for that subgroup, whereas a statistically favorable result for the overall population would lead to a claim that includes both biomarker subgroups. The latter setting is problematic when biomarker-negative patients truly do not benefit from the experimental regimen. When it is prespecified that biomarker-negative patients should not be included in the primary analysis of treatment effect in biomarker-positive patients because of the likelihood that treatment effects would differ between the 2 subgroups, it is logically inconsistent to include biomarker-positive patients in the primary analysis of treatment effect in biomarker-negative patients.

Distribution pattern of Plasmodium falciparum chloroquine transporter (pfcrt) gene haplotypes in Sri Lanka 1996-2006.

Widespread antimalarial resistance has been a barrier to malaria elimination efforts in Sri Lanka. Analysis of genetic markers in historic parasites may uncover trends in the spread of resistance. We examined the frequency of Plasmodium falciparum chloroquine transporter (pfcrt; codons 72-76) haplotypes in Sri Lanka in 1996-1998 and 2004-2006 using a high-resolution melting assay. Among 59 samples from 1996 to 1998, we detected the SVMNT (86%), CVMNK (10%), and CVIET (2%) haplotypes, with a positive trend in SVMNT and a negative trend in CVMNK frequency (P = 0.004) over time. Among 24 samples from 2004 to 2006, we observed only the SVMNT haplotype. This finding indicates selection for the SVMNT haplotype over time and its possible fixation in the population.

Statistical efficiency in multiple-to-one comparison trials with optimal allocation ratio.

This paper discusses multiple-to-one comparison trials testing a multivalent vaccine product against multiple comparators with respect to immunologic responses. An optimal subject allocation ratio between the multivalent vaccine group and any of the comparators is introduced. This optimal ratio leads to higher statistical efficiency in terms of savings in sample size compared to equal allocation or any other allocation ratios. Several trial design scenarios are considered including assumptions of equal standardized effect size, unequal variance, and unequal standardized effect sizes of the multivalent vaccines versus the multiple comparators.

Latent class joint model of ovarian function suppression and DFS for premenopausal breast cancer patients.

Breast cancer is the leading cancer in women of reproductive age; more than a quarter of women diagnosed with breast cancer in the US are premenopausal. A common adjuvant treatment for this patient population is chemotherapy, which has been shown to cause premature menopause and infertility with serious consequences to quality of life. Luteinizing-hormone-releasing hormone (LHRH) agonists, which induce temporary ovarian function suppression (OFS), has been shown to be a useful alternative to chemotherapy in the adjuvant setting for estrogen-receptor-positive breast cancer patients. LHRH agonists have the potential to preserve fertility after treatment, thus, reducing the negative effects on a patient's reproductive health. However, little is known about the association between a patient's underlying degree of OFS and disease-free survival (DFS) after receiving LHRH agonists. Specifically, we are interested in whether patients with lower underlying degrees of OFS (i.e. higher estrogen production) after taking LHRH agonists are at a higher risk for late breast cancer events. In this paper, we propose a latent class joint model (LCJM) to analyze a data set from International Breast Cancer Study Group (IBCSG) Trial VIII to investigate the association between OFS and DFS. Analysis of this data set is challenging due to the fact that the main outcome of interest, OFS, is unobservable and the available surrogates for this latent variable involve masked event and cured proportions. We employ a likelihood approach and the EM algorithm to obtain parameter estimates and present results from the IBCSG data analysis.

An accelerated failure time mixture cure model with masked event.

We extend the Dahlberg and Wang (Biometrics 2007, 63, 1237-1244) proportional hazards (PH) cure model for the analysis of time-to-event data that is subject to a cure rate with masked event to a setting where the PH assumption does not hold. Assuming an accelerated failure time (AFT) model with unspecified error distribution for the time to the event of interest, we propose rank-based estimating equations for the model parameters and use a generalization of the EM algorithm for parameter estimation. Applying our proposed AFT model to the same motivating breast cancer dataset as Dahlberg and Wang (Biometrics 2007, 63, 1237-1244), our results are more intuitive for the treatment arm in which the PH assumption may be violated. We also conduct a simulation study to evaluate the performance of the proposed method.

PECAM-1 modulates thrombin-induced tissue factor expression on endothelial cells.

Platelet endothelial cell adhesion molecule-1 (PECAM-1) (CD31) is known to inhibit platelet function and thrombus formation. The mechanisms involved in PECAM-1's roles as a modulator of hemostasis are still not completely understood. We examined the role of PECAM-1 as a regulator of tissue factor (TF) expression, a known important inducer of thrombosis. Wildtype and CD31KO mice underwent transient (30 min) renal ischemia followed by 24 h re-perfusion and their kidneys assessed for apoptosis, fibrin formation, and tissue factor expression. CD31KO mice exhibited increased tubular epithelial and endothelial apoptosis, increased fibrin deposition, and tissue factor expression. Human umbilical vein endothelial cells (HUVEC) transfected with antisense (AS) PECAM-1 oligonucleotides to downregulate PECAM-1 expression, exhibited greater induction of TF mRNA and protein expression as well as increased expression and nuclear localization of the transcription factor Egr-1 compared to scrambled AS PECAM-1 (Scr)-treated HUVEC following thrombin stimulation. TF induction was found to be mediated through thrombin receptor PAR-1 and the Galphai/o subunit of G-protein, confirmed by PAR-1 antagonist and pertussis toxin inhibition respectively. Thrombin-mediated TF induction was dependent on Rho Kinase activity, phosphorylation of p38(MAPK) and p85 & Akt dephosphorylation. The inverse correlation of PI3K-Akt phosphorylation with p38 (MAPK) phosphorylation was confirmed by pharmacological inhibition. These studies suggest that PECAM-1 is involved in regulating a signaling pathway, affecting PI3K and Akt activation, p38 (MAPK) phosphorylation, which in turn, affects Egr-1 expression and nuclear translocation, ultimately affecting TF expression. These findings provide new insights into the action of PECAM-1 as a modulator of thrombosis.

Reversal of renal fibrosis, inflammation, and glomerular hypertrophy by kallikrein gene delivery.

Evidence suggests that the progression of renal fibrosis is a reversible process. Because inflammation plays a crucial role in the development of renal injury, we examined the effect of kallikrein and activation of the kinin B2 receptor on the reversal of salt-induced inflammation and renal fibrosis in Dahl salt-sensitive (DSS) rats. Four weeks after high salt loading, when renal injury was apparent, adenovirus harboring the human tissue kallikrein gene was injected into DSS rats. To determine the role of the B2 receptor in mediating the actions of kallikrein, icatibant, a kinin B2 receptor antagonist, was infused with kallikrein gene delivery. Two weeks after adenovirus injection, salt-induced glomerular sclerosis, tubular protein cast formation, and monocyte/ macrophage accumulation in the kidney were notably reversed by kallikrein. Decreased intercellular adhesion molecule-1 expression paralleled this observation. Kallikrein gene delivery also dramatically reduced collagens I, III, and IV and reticulin deposition, accompanied by a decline in myofibroblast accumulation and transforming growth factor-beta(1) expression. Moreover, kallikrein reversed salt-induced glomerular hypertrophy and inhibited the increase in levels of the cell cycle-inhibitory proteins p21 and p27. These protective actions of kallikrein were abolished by icatibant, indicating a B2 receptor-mediated event. In addition, kallikrein protected against salt-induced renal injury by diminishing urinary protein and blood urea nitrogen levels. Furthermore, kallikrein gene delivery restored nitric oxide production and suppressed NADH oxidase activity and superoxide generation. These results indicate that tissue kallikrein, through the kinin B2 receptor, reverses salt-induced inflammation, renal fibrosis, and glomerular hypertrophy via suppression of oxidative stress.

Tissue kallikrein attenuates salt-induced renal fibrosis by inhibition of oxidative stress.

BACKGROUND: High salt intake induces hypertension, cardiac hypertrophy, and progressive renal damage. Progressive renal injury is the consequence of a process of destructive fibrosis. Using gene transfer approach, we have shown that the tissue kallikrein-kinin system (KKS) plays an important role in protection against renal injury in several hypertensive rat models. In this study, we further investigated the effect and potential mechanisms mediated by kallikrein on salt-induced renal fibrosis. METHODS: Adenovirus harboring the human tissue kallikrein gene was delivered intravenously into Dahl salt-sensitive (DSS) rats on a high salt diet for 4 weeks. Two weeks after gene delivery, the effect of kallikrein on renal fibrosis was examined by biochemical and histologic analysis. RESULTS: Kallikrein gene delivery resulted in reduced blood urea nitrogen (BUN), urinary protein and albumin levels in DSS rats on a high salt diet. Expression of recombinant human tissue kallikrein was detected in the sera and urine of rats injected with the kallikrein gene. Histologic investigation showed that kallikrein gene delivery significantly reduced glomerular and tubular fibrosis scores and collagen deposition, as well as renal cell proliferation, compared to rats on a high salt diet injected with control virus. Kallikrein gene transfer significantly increased nitric oxide and cyclic guanosine monophosphate (cGMP) levels in conjunction with reduced salt-induced nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate (NADH/NADPH) oxidase activity, superoxide production, transforming growth factor-beta1 (TGF-beta1) mRNA and protein levels, and TGF-beta1 immunostaining. CONCLUSION: These results indicate that tissue kallikrein protects against renal fibrosis in hypertensive DSS rats through increased nitric oxide bioavailability and suppression of oxidative stress and TGF-beta expression.