Phase I and Phase II Objective Response Rates are Correlated in Pediatric Cancer Trials: An Argument for Better Clinical Trial Efficiency

Phase I trials and therapeutic intent in the age of precision oncology: What is a patient's chance of response?

The advancement of therapeutic strategies in oncology such as precision oncology has generated significant interest in better estimating the response of modern phase I cancer clinical trials. These estimates have varied widely. In this commentary, we provide an umbrella review of phase I response rates and discuss methodological reasons for variation in prior estimates which include limited use of unpublished data, the inclusion of expansion cohorts that artificially raise response rates of cumulative response rates, varying enrolment of haematologic malignancies, and increased next in class drugs.

Predictors of Success of Phase II Pediatric Oncology Clinical Trials

BACKGROUND

There are limited data to predict which novel childhood cancer therapies are likely to be successful. To help rectify this, we sought to identify the factors that impact the success of phase II clinical trials for pediatric malignancies.

MATERIALS AND METHODS

We examined the impact of 24 preclinical and trial design variables for their influence on 132 phase II pediatric oncology clinical trials. Success was determined by an objective assessment of patient response, with data analyzed using Fisher's exact test, Pearson's chi-square test, and logistic regression models.

RESULTS

Trials that evaluated patients with a single histological cancer type were more successful than those that assessed multiple different cancer types (68% vs. 47%, 27%, and 17% for 1, 2-3, 4-7, and 8+; p < .005). Trials on liquid or extracranial solid tumors were more successful than central nervous system or combined trials (70%, 60%, 38%, and 24%; p < .005), and trials of combination therapies were more successful than single agents (71% vs. 28%; p < .005). Trials that added therapies to standard treatment backbones were more successful than trials testing novel therapies alone or those that incorporated novel agents (p < .005), and trials initiated based on the results of adult studies were less likely to succeed (p < .05). For 61% of trials (80/132), we were unable to locate any relevant preclinical findings to support the trial. When preclinical studies were carried out (52/132), there was no evidence that the conduct of any preclinical experiments made the trial more likely to succeed (p < .005).

CONCLUSION

Phase II pediatric oncology clinical trials that examine a single cancer type and use combination therapies have the highest possibility of clinical success. Trials building upon a standard treatment regimen were also more successful. The conduct of preclinical experiments did not improve clinical success, emphasizing the need for a better understanding of the translational relevance of current preclinical testing paradigms.

IMPLICATIONS FOR PRACTICE

To improve the clinical outcomes of phase II childhood cancer trials, this study identified factors impacting clinical success. These results have the potential to impact not only the design of future clinical trials but also the assessment of preclinical studies moving forward. This work found that trials on one histological cancer type and trials testing combination therapies had the highest possibility of success. Incorporation of novel therapies into standard treatment backbones led to higher success rates than testing novel therapies alone. This study found that most trials had no preclinical evidence to support initiation, and even when preclinical studies were available, they did not result in improved success.

Evolving paradigms for new agent development in pediatric oncology

PURPOSE OF REVIEW

To discuss considerations of new paradigms for clinical drug development in pediatric oncology that incorporate our expanding knowledge and complexity of molecular alterations associated with cancer; advances in cancer immunology and cellular therapy; the increasing number of new anticancer drugs, therapeutic approaches, and potential combinations; and recent initiatives by regulatory agencies to improve access to safe and effective therapies.

RECENT FINDINGS

Cancer in children and adolescents is a rare event with significant long-term impact on individuals and society. Using multimodality therapy, stratified by patient and disease characteristics, the cure rate for childhood cancer exceeds 80%. Cancer genomics has transformed anticancer drug development. Understanding the genetic basis of pediatric cancers and the use of genomics for risk stratification has changed the focus of drug development from cytotoxic drugs to targeted therapeutic approaches. Advances in cancer immunology, immune checkpoint blockade, and cellular therapy offer novel approaches to harness T cells to treat cancer. To improve the outcome for children and adolescents with cancer and accelerate drug development, understanding drug and target interactions in preclinical models of pediatric cancer should be coupled with efficient clinical trial designs that incorporate biomarker selection, assessment of toxicity and drug exposure, and improved measures of response.

SUMMARY

Clinical trials for children and adolescents with cancer evaluate cytotoxic drugs, molecularly target drugs, immunotherapy as well as combination therapies. The framework for oncology clinical trials will continually adapt to improve efficiency of trials and evaluate new therapeutic approaches.

A comparison of safety and efficacy of cytotoxic versus molecularly targeted drugs in pediatric phase I solid tumor oncology trials

BACKGROUND

Prior reviews of phase I pediatric oncology trials involving primarily cytotoxic agents have reported objective response rates (ORRs) and toxic death rates of 7.9-9.6% and 0.5%, respectively. These data may not reflect safety and efficacy in phase I trials of molecularly targeted (targeted) drugs.

METHODS

A systematic review of pediatric phase I solid tumor trials published in 1990-2013 was performed. The published reports were evaluated for patient characteristics, toxicity information, and response numbers.

RESULTS

A total of 143 phase I pediatric clinical trials enrolling 3,896 children involving 53 targeted and 48 cytotoxic drugs were identified. A meta-analysis demonstrated that the ORR is 2.1-fold higher with cytotoxic drugs (0.066 vs. 0.031 per subject; P = 0.007). By contrast, the pooled estimate of the stable disease rate (SDR) is similar for cytotoxic and targeted drugs (0.2 vs. 0.23 per subject; P = 0.27).  The pooled estimate of the dose-limiting toxicity rate is 1.8-fold larger with cytotoxic drugs (0.24 vs. 0.13 per subject; P = 0.0003). The hematologic grade 3-4 (G3/4) toxicity rate is 3.6-fold larger with cytotoxic drugs (0.43 vs. 0.12 per treatment course; P = 0.0001); however, the nonhematologic G3/4 toxicities and toxic deaths occur at similar rates for cytotoxic and targeted drugs.

CONCLUSIONS

In phase I pediatric solid tumor trials, ORRs were significantly higher for cytotoxic versus targeted agents. SDRs were similar in targeted and cytotoxic drug trials. Patients treated with cytotoxic agents were more likely to experience hematologic G3/4 toxicities than those patients receiving targeted drugs.