Biomedical subjects

Andrew Stone

Publications and source records attributed to Andrew Stone.

4 recordsLinked to original sources

PubMed2006

Improving the design of phase II trials of cytostatic anticancer agents.

This paper examines the design of phase II trials in oncology and recommends departing from the traditional uncontrolled trial design. Entrance into phase II clinical evaluation represents a key milestone in the development of any new cancer therapy. As novel molecular-targeted therapies are introduced, whose primary action is to slow the growth of tumors, it will be important to ensure that the clinical trial design will effectively capture any clinical benefit of these agents. The objective of a phase II trial should, in addition to identifying active therapies, be extended to identifying those that are likely to be successful in pivotal trials. It is therefore necessary to quantify the likelihood of either incorrectly halting the development of an active agent or continuing development of an ineffective agent. We believe only randomized studies with comparative intent and including a concurrent active control, can reliably assess these risks corresponding to significance and power. Given that the objective of phase II studies is to identify promising treatments, it is important not be constrained by conventional levels of significance. This paper will review the various approaches to phase II trial design in oncology and provide a framework for fully powered randomized trials of a moderate size. For example, a randomized trial of just 100 patients could lead to the termination of development of 90% of inactive agents whereas at least 80% of agents with a meaningful and realistic increase in progression-free survival would be identified for confirmatory study. We believe randomized studies with progression-free survival endpoints are the most powerful and economical method of determining the clinical activity of new cytostatic agents.

Algorithms↗

PubMed2006

Optimizing randomized phase II trials assessing tumor progression.

The traditional development paradigm for phase II trials in oncology has been challenged in recent years by the introduction of cytostatic therapies. These agents slow the growth of tumors rather than cause high rates of shrinkage, this argues for the use of endpoints that measure growth inhibition such as progression free survival. We have previously argued the need for randomized trials in this setting. Here we discuss methodological solutions to enhance the development decision at the end of phase II in the context of progression endpoints employed in randomized trials. There are well recognized issues associated with progression endpoints relating to bias in the timing and interpretation of assessments. In this paper we present design and analysis solutions that will minimize bias by using methods that are either partially or completely time independent. We also discuss other design features to maximize the information yielded in a phase II setting. We advocate the creation of progression endpoints that utilize all available progression data rather than early fixed time-point analyses and show that little is to be gained by assessing progression status any more frequently than would be required in routine clinical practice. Such design and analysis measures will optimize the development decision made at the end of phase II clinical evaluation.

Algorithms↗

PubMed2006

Comparative study into the robustness of compartmental modeling and model-free analysis in DCE-MRI studies.

PURPOSE: To evaluate and compare the reproducibility of the preferred phenomenological parameter IAUC60 (initial area under the time-concentration curve [IAUC] defined over the first 60 seconds postenhancement) with the preferred modeling parameter (K(trans)), as derived using two simple models, in abdominal and cerebral data collected in typical Phase I clinical trial conditions. MATERIALS AND METHODS: Dynamic contrast enhanced MRI (DCE-MRI) time series were acquired at two imaging centers from a group of patients with abdominal tumors and a group with gliomas. At both imaging centers, precontrast T1 was calculated using a variable flip angle three-dimensional spoiled gradient echo acquisition that was used to quantify tissue contrast agent concentration, allowing voxelwise definition of summary DCE-MRI parameters. RESULTS: A comparison of reproducibility showed that there was no statistically significant difference in reproducibility between IAUC60 and K(trans), although there was a trend towards better reproducibility for K(trans) (P = 0.0782). The 95% confidence intervals (CIs) for individual changes showed that for IAUC60 and K(trans), changes in excess of 47% and 31%, respectively, are outside the range of normal variability. CONCLUSION: Although modeling is more complex and more computationally intensive than an IAUC parameterization, our data suggest this approach to be preferable to a model-free approach since it provides greater physiological insight without a reduction in statistical power for Phase I/II clinical drug trials.

Abdominal Neoplasms↗

PubMed2004

Magnetic resonance imaging measurements of the response of murine and human tumors to the vascular-targeting agent ZD6126.

PURPOSE: ZD6126 is a novel vascular targeting agent currently undergoing clinical evaluation. It acts by destabilizing the microtubulin of fragile and proliferating neoendothelial cells in tumors. The drug leads to blood vessel congestion, the selective destruction of the vasculature, and extensive necrosis in experimental tumors. The aim of the study reported here was to assess the ability of dynamic contrast enhanced magnetic resonance imaging (MRI) to measure the antivascular effects of ZD6126 in tumors. EXPERIMENTAL DESIGN: The work was carried out in mice bearing C38 colon adenocarcinoma and in patients with advanced cancers. MRI was performed before and 6 h (human tumors) or 24 h (C38 tumors) after i.v. drug administration. Contrast agent (gadolinium diethylenetriaminepentaacetate) enhancement was characterized by the initial area under the gadolinium diethylenetriaminepentaacetate uptake versus time curve (IAUC). IAUC reflects blood flow, vascular permeability, and the fraction of interstitial space. RESULTS: The median IAUC was reduced in all C38 tumors after ZD6126 administration [by 6-48% at 50 mg/kg (n = 3)], 58-91% at 100 mg/kg (n = 4), and 11-93% at 200 mg/kg (n = 6). In contrast, the administration of vehicle only led to no consistent change in median IAUC (n = 4). The ZD6126-induced changes in median IAUC appeared to be dose dependent (P = 0.045). No ZD6126-induced changes were apparent in murine muscle. Similar effects were seen in preliminary data from human tumors (11 tumors studied, 9 patients). At doses of 80 mg/m(2) and higher, the median IAUC post-ZD6126 treatment was reduced in all of the tumors studied (8 tumors, 6 patients) to 36-72% from the baseline value. There was a significant trend of increasing reductions with increasing exposure (P < 0.01). No drug-induced changes in human muscle or spleen IAUC were apparent. The reproducibility of the median IAUC parameter was investigated in patients. In 19 human tumors (measured in 19 patients) inter- and intratumor coefficients of variation were 64 and 18%. CONCLUSIONS: The contrast enhanced-MRI measured median IAUC is a useful end point for quantifying ZD6126 antivascular effects in human tumors.

Angiogenesis Inhibitors↗