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Biomedical subjects

Peter F Thall

Publications and source records attributed to Peter F Thall.

At least 19 recordsLinked to original sources
PubMed2006

Expression of Bcl-2 in gastrointestinal stromal tumors: correlation with progression-free survival in 81 patients treated with imatinib mesylate.

BACKGROUND: The natural history of gastrointestinal stromal tumor (GIST) has been revolutionized by imatinib mesylate (imatinib) therapy. Before imatinib, Bcl-2 expression in GIST was associated with a worse prognosis or added no additional prognostic value. To the authors' knowledge, the current study is the first to evaluate Bcl-2 expression in pre-imatinib GIST tissue samples as a prognostic marker of progression-free survival (PFS) time in patients treated with imatinib. METHODS: The cases of 81 patients with GIST who were evaluated between December 15, 2000 and September 1, 2001 were retrospectively reviewed. Clinicopathologic variables were reviewed. GIST cell morphology and patterns of Bcl-2 expression were described. The methods of Kaplan-Meier and the Cox proportional hazards regression model were used for statistical analysis. RESULTS: Sixty-one (75%) patients had tumors that expressed Bcl-2, and 20 (25%) patients had tumors that were negative for Bcl-2. All epithelioid tumors (n = 12) expressed Bcl-2 and tumors with mixed morphology exhibited Bcl-2 expression in the epithelioid component. A trend toward longer PFS for patients whose tumors expressed Bcl-2 at a greater immunohistochemical intensity was observed (20.6 mos for no Bcl-2 expression; 28.3 mos for 1++Bcl-2 expression; 31.9 mos for 1.5++Bcl-2 expression; 40.8 mos for 2++Bcl-2 expresssion; and 35.9 mos for 3++Bcl-2 expression). CONCLUSIONS: In contrast to studies performed in the preimatinib era, in which Bcl-2 was found to be a negative prognostic indicator, the current study suggests a trend toward better PFS with increasing Bcl-2 expression level in GISTs from patients subsequently treated with imatinib. Larger studies may help elucidate the influence of Bcl-2 expression on PFS after therapy with imatinib.

Adult↗
PubMed2006

Continuous Bayesian adaptive randomization based on event times with covariates.

In comparative clinical trials, the randomization probabilities may be unbalanced adaptively by utilizing the interim data available at each patient's entry time to favour the treatment or treatments having comparatively superior outcomes. This is ethically appealing because, on average, more patients are assigned to the more successful treatments. Consequently, physicians are more likely to enroll patients onto trials where the randomization is outcome-adaptive rather than balanced in the conventional manner. Outcome-adaptive methods based on a binary variable may be applied by reducing an event time to the indicator of the event's occurrence within a predetermined time interval. This results in a loss of information, however, since it ignores the censoring times of patients who have not experienced the event but whose evaluation interval is not complete. This paper proposes and compares exact and approximate Bayesian outcome-adaptive randomization procedures based on time-to-event outcomes. The procedures account for baseline prognostic covariates, and they may be applied continuously over the course of the trial. We illustrate these methods by application to a phase II selection trial in acute leukaemia. A simulation study in the context of this trial is presented.

Antineoplastic Agents↗
PubMed2006

Adaptive dose selection using efficacy-toxicity trade-offs: illustrations and practical considerations.

The purpose of this paper is to describe and illustrate an outcome-adaptive Bayesian procedure, proposed by Thall and Cook (2004), for assigning doses of an experimental treatment to successive cohorts of patients. The method uses elicited (efficacy, toxicity) probability pairs to construct a family of trade-off contours that are used to quantify the desirability of each dose. This provides a basis for determining a best dose for each cohort. The method combines the goals of conventional Phase I and Phase II trials, and thus may be called a "Phase I-II" design. We first give a general review of the probability model and dose-finding algorithm. We next describe an application to a trial of a biologic agent for treatment of acute myelogenous leukemia, including a computer simulation study to assess the design's average behavior. To illustrate how the method may work in practice, we present a cohort-by-cohort example of a particular trial. We close with a discussion of some practical issues that may arise during implementation.

Algorithms↗
PubMed2006

A geometric approach to comparing treatments for rapidly fatal diseases.

In therapy of rapidly fatal diseases, early treatment efficacy often is characterized by an event, "response," which is observed relatively quickly. Since the risk of death decreases at the time of response, it is desirable not only to achieve a response, but to do so as rapidly as possible. We propose a Bayesian method for comparing treatments in this setting based on a competing risks model for response and death without response. Treatment effect is characterized by a two-dimensional parameter consisting of the probability of response within a specified time and the mean time to response. Several target parameter pairs are elicited from the physician so that, for a reference covariate vector, all elicited pairs embody the same improvement in treatment efficacy compared to a fixed standard. A curve is fit to the elicited pairs and used to determine a two-dimensional parameter set in which a new treatment is considered superior to the standard. Posterior probabilities of this set are used to construct rules for the treatment comparison and safety monitoring. The method is illustrated by a randomized trial comparing two cord blood transplantation methods.

Bayes Theorem↗
PubMed2005

Covariate-adjusted adaptive randomization in a sarcoma trial with multi-stage treatments.

We present a Bayesian design for a multi-centre, randomized clinical trial of two chemotherapy regimens for advanced or metastatic unresectable soft tissue sarcoma. After randomization, each patient receives up to four stages of chemotherapy, with the patient's disease evaluated after each stage and categorized on a trinary scale of severity. Therapy is continued to the next stage if the patient's disease is stable, and is discontinued if either tumour response or treatment failure is observed. We assume a probability model that accounts for baseline covariates and the multi-stage treatment and disease evaluation structure. The design uses covariate-adjusted adaptive randomization based on a score that combines the patient's probabilities of overall treatment success or failure. The adaptive randomization procedure generalizes the method proposed by Thompson (1933) for two binomial distributions with beta priors. A simulation study of the design in the context of the sarcoma trial is presented.

Antineoplastic Agents↗
PubMed2005

Prognostic factors for outcomes of patients with refractory or relapsed acute myelogenous leukemia or myelodysplastic syndromes undergoing allogeneic progenitor cell transplantation.

Allogeneic progenitor cell transplantation is the only curative therapy for patients with refractory acute myelogenous leukemia or myelodysplastic syndromes. To identify prognostic factors in these patients, we performed a retrospective analysis of transplantation outcomes. Patients were selected if they had undergone an allogeneic transplantation between January 1988 and January 2002 and were not in remission or first untreated relapse at the time of transplantation. A total of 135 patients were identified. The median age was 49.5 years (range, 19-75 years). At the time of transplantation, 39.3% of patients had not responded to induction therapy, 37% had not responded to first salvage therapy, and 23.7% were beyond first salvage. Forty-one patients (30%) received unrelated donor progenitor cells. Eighty patients (59%) received either a reduced-intensity or a nonmyeloablative regimen. A total of 104 (77%) of 135 patients died, with a median survival time of 4.9 months (95% confidence interval, 3.9-6.6 months). The median progression-free survival was 2.9 months (95% confidence interval, 2.5-4.2 months). A Cox regression analysis showed that Karnofsky performance status, peripheral blood blasts, and tacrolimus exposure during the first 11 days after transplantation were predictive of survival. These data support the use of allogeneic transplantation for patients with relapsed or refractory acute myelogenous leukemia/myelodysplastic syndromes and suggest that optimal immune suppression early after transplantation is essential for long-term survival even in patients with refractory myeloid leukemias.

Adult↗
PubMed2005

Determining a maximum-tolerated schedule of a cytotoxic agent.

Most phase I clinical trials are designed to determine a maximum-tolerated dose (MTD) for one initial administration or treatment course of a cytotoxic experimental agent. Toxicity usually is defined as the indicator of whether one or more particular adverse events occur within a short time period from the start of therapy. However, physicians often administer an agent to the patient repeatedly and monitor long-term toxicity due to cumulative effects. We propose a new method for such settings. It is based on the time to toxicity rather than a binary outcome, and the goal is to determine a maximum-tolerated schedule (MTS) rather than a conventional MTD. The model and method account for a patient's entire sequence of administrations, with the overall hazard of toxicity modeled as the sum of a sequence of hazards, each associated with one administration. Data monitoring and decision making are done continuously throughout the trial. We illustrate the method with an allogeneic bone marrow transplantation (BMT) trial to determine how long a recombinant human growth factor can be administered as prophylaxis for acute graft-versus-host disease (aGVHD), and we present a simulation study in the context of this trial.

Algorithms↗
PubMed2005

Monitoring event times in early phase clinical trials: some practical issues.

BACKGROUND: In many early phase clinical trials it is scientifically inappropriate or logistically infeasible to characterize patient outcome as a binary variable. In such settings, it often is more natural to construct early stopping rules based on time-to-event variables. This type of design may involve a variety of complications, however. PURPOSE: The purpose of this paper is to illustrate by example how one may deal with various complications that may arise when monitoring time-to-event outcomes in an early phase clinical trial. METHODS: We present a series of Bayesian designs for a phase II clinical trial in kidney cancer. Each design includes a procedure for monitoring the times to a severe adverse event, disease progression and death. The first design, which is the simplest, is based on the time to failure, defined as any of the three events, assuming exponentially distributed failure times with an inverse gamma prior on the mean. This design is compared by simulation to the CMAP design (Cheung and Thall, Biometrics, 2002; 58: 89-97). The model and monitoring procedure are then extended successively to accommodate several common practical complications, and we also study the method's robustness. RESULTS: Our simulations show that 1) one may apply the monitoring rule periodically, rather than continuously, without a substantive degradation of the design's reliability; 2) it is very important to account for interval censoring due to periodic evaluation of disease status; 3) it is important to account for the effect of disease progression on the subsequent death rate; 4) conducting a randomized trial presents little additional difficulty and provides unbiased comparisons; and 5) the exponential-inverse gamma model is surprisingly robust in most cases. LIMITATIONS: The methods discussed here do not account for patient heterogeneity. This is an important but complex issue that may be dealt with by extending the models and methods given here to accommodate patient covariates and treatment-covariate interaction. CONCLUSIONS: Bayesian procedures for monitoring time-to-event outcomes offer a practical way to conduct a variety of early phase trials. Considerable care must be given, however, to modeling the important aspects of the trial at hand, and to calibrating the prior and the design parameters to ensure that the design will have good operating characteristics.

Bayes Theorem↗
PubMed2005

Some ethical issues in phase II trials in acute leukemia.

This paper addresses several scientific and ethical issues that arise in the design and conduct of phase II clinical trials of experimental therapies. Although we discuss chemotherapy trials in acute leukemia, the issues pertain to a much larger class of early-phase clinical trials. Our focus is on the manner in which numerical values of standard and targeted response rates of a statistical design are specified, the number of interim tests that are applied, and the effects of these design features on early stopping probabilities and the treatments that patients actually receive. These points are illustrated by numerical comparisons of alternative designs for a particular phase II trial of a new drug for relapsed or refractory acute myelogenous leukemia. We show that statistical designs that target inappropriately low response rates or that apply early stopping rules too infrequently are at odds with good statistical and medical practice and that such designs often provide less benefit to the patients in the trial than would be obtained by simply treating all patients with standard therapy. The general conclusions are that statistical designs have both scientific and ethical implications, and that science, statistics, and ethics cannot be treated as separate issues.

Acute Disease↗
PubMed2004

Cohort analysis of patients with localized, high-risk, extremity soft tissue sarcoma treated at two cancer centers: chemotherapy-associated outcomes.

PURPOSE: Patients with American Joint Committee on Cancer stage III soft tissue sarcoma (STS) have high risks of distant recurrence and death. The role of chemotherapy for these patients remains controversial despite several randomized trials and a meta-analysis. METHODS: We reviewed the treatments and outcomes of 674 consecutive adult patients presenting with primary stage III extremity STS between 1984 and 1999. Pre- or postoperative doxorubicin-based chemotherapy was used in a nonrandomized fashion in approximately half of this high-risk population. The objective of this review was to evaluate the impact of chemotherapy while accounting for known prognostic variables. RESULTS: Among 674 patients, 338 (50%) were treated with local therapy only, and 336 (50%) were treated with local therapy plus chemotherapy. The median follow-up for survivors was 6.1 years. Five-year local and distant recurrence-free interval probabilities were 83% and 56%, respectively, for the two groups combined. The 5-year disease-specific survival (DSS) rate was 61%. Cox regression analyses showed a time-varying effect associated with chemotherapy. During the first year, the hazard ratio associated with DSS for patients treated with chemotherapy versus no chemotherapy was 0.37 (95% CI, 0.20 to 0.69; P = .002). Thereafter, this hazard ratio was 1.36 (95% CI, 1.02 to 1.81; P = .04). CONCLUSION: It seems that the clinical benefits associated with doxorubicin-based chemotherapy in patients with high-risk extremity STS are not sustained beyond 1 year. These results suggest that caution should be used in the interpretation of randomized clinical trials of adjuvant chemotherapy that seem to demonstrate clinical benefits with relatively short-term follow-up.

Adult↗
PubMed2004

Phase I trial of preoperative doxorubicin-based concurrent chemoradiation and surgical resection for localized extremity and body wall soft tissue sarcomas.

PURPOSE: The primary objective of this phase I trial was to define the maximum-tolerated dose of continuous-infusion doxorubicin administered with standard preoperative radiation for patients with localized, potentially resectable soft tissue sarcomas of the extremities or body wall. PATIENTS AND METHODS: Twenty-seven patients with radiographically resectable intermediate- or high-grade soft tissue sarcomas were treated. Preoperative external-beam radiation was administered in 25 2-Gy fractions (total dose, 50 Gy). Concurrent continuous-infusion doxorubicin was administered by an initial bolus (4 mg/m(2)) and subsequent 4-day continuous infusion (12.5, 15.0, 17.5, or 20.0 mg/m(2)/wk). Radiographic restaging was performed 4 to 7 weeks after chemoradiation, and patients with localized disease underwent surgical resection. RESULTS: Chemoradiation was completed as an outpatient procedure in 25 patients (93%). The maximum-tolerated dose of continuous-infusion doxorubicin combined with standard preoperative radiation was 17.5 mg/m(2)/wk; at this dose level, seven (30%) of 23 patients had grade 3 dermatologic toxicity. Macroscopically complete resection (R0 or R1) was performed in all 26 patients who underwent surgery. Among 22 patients who were treated with doxorubicin 17.5/mg/m(2)/wk with concurrent radiation and subsequent surgery, 11 patients (50%) had 90% or greater tumor necrosis, including two patients who had complete pathologic responses. CONCLUSION: Preoperative doxorubicin-based chemoradiation appears safe and feasible. The maximum-tolerated dose of continuous-infusion doxorubicin with standard preoperative radiation was 17.5 mg/m(2)/wk. Pathologic response rates with this regimen are encouraging.

Adolescent↗
PubMed2004

Platelet-derived growth factor receptor inhibitor imatinib mesylate and docetaxel: a modular phase I trial in androgen-independent prostate cancer.

PURPOSE: To study the platelet-derived growth factor receptor (PDGFR) inhibitor imatinib mesylate in androgen-independent prostate cancer (AIPC), alone and in combination with docetaxel, we designed a modular phase I trial. Our goals were to (1) evaluate the toxicity and maximum-tolerated dose of docetaxel with imatinib, and (2) evaluate the decline of prostate-specific antigen (PSA) induced by imatinib alone, and imatinib and docetaxel. PATIENTS AND METHODS: Twenty-eight men with AIPC and bone metastases were enrolled to receive imatinib 600 mg daily lead-in for 30 days, then imatinib 600 mg daily and one of six possible doses of docetaxel weekly for 4 weeks every 6 weeks. RESULTS: During the imatinib lead-in module, one dose-limiting toxicity (DLT) event was observed, while two (7%) of 28 had PSA decline (both < 50%). With imatinib and docetaxel, cycle 1 DLT was found in three of 12 patients at docetaxel 30 mg/m(2), in three of four patients at docetaxel 45 mg/m(2), and in five of six patients at docetaxel 35 mg/m(2). DLTs (n = 40 total events) were principally fatigue (35%) and nausea (20%). Eight (38%) of 21 had PSA decline greater than 50%, and six (29%) of 21 had PSA decline less than 50%. Serial PSA declines beyond 18 months were observed. PDGFR-expressing tumor declined on serial bone marrow biopsies with combination therapy alone. CONCLUSION: With imatinib 600 mg daily, the maximum-tolerated dose of docetaxel was determined to be 30 mg/m(2) weekly for 4 weeks every 6 weeks. Long-term responses were observed. The role of imatinib in modulating outcomes to docetaxel in AIPC is being tested in a randomized phase II trial.

Adult↗
PubMed2004

Phase I study of the farnesyltransferase inhibitor lonafarnib with paclitaxel in solid tumors.

PURPOSE: To establish the maximum tolerated dose of lonafarnib, a novel farnesyltransferase inhibitor, in combination with paclitaxel in patients with solid tumors and to characterize the safety, tolerability, dose-limiting toxicity, and pharmacokinetics of this combination regimen. EXPERIMENTAL DESIGN: In a Phase I trial, lonafarnib was administered p.o., twice daily (b.i.d.) on continuously scheduled doses of 100 mg, 125 mg, and 150 mg in combination with i.v. paclitaxel at doses of 135 mg/m(2) or 175 mg/m(2) administered over 3 h on day 8 of every 21-day cycle. Plasma paclitaxel and lonafarnib concentrations were collected at selected time points from each patient. RESULTS: Twenty-four patients were enrolled; 21 patients were evaluable. The principal grade 3/4 toxicity was diarrhea (5 of 21 patients), which was most likely due to lonafarnib. dose-limiting toxicities included grade 3 hyperbilirubinemia at dose level 3 (100 mg b.i.d. lonafarnib and 175 mg/m(2) paclitaxel); grade 4 diarrhea and grade 3 peripheral neuropathy at dose level 3A (125 mg b.i.d. lonafarnib and 175 mg/m(2) paclitaxel); and grade 4 neutropenia with fever and grade 4 diarrhea at level 4 (150 mg b.i.d. lonafarnib and 175 mg/m(2) paclitaxel). The maximum tolerated dose established by the continual reassessment method was lonafarnib 100 mg b.i.d. and paclitaxel 175 mg/m(2). Paclitaxel appeared to have no effect on the pharmacokinetics of lonafarnib. The median duration of therapy was eight cycles, including seven cycles with paclitaxel. Six of 15 previously treated patients had a durable partial response, including 3 patients who had previous taxane therapy. Notably, two of five patients with taxane-resistant metastatic non-small cell lung cancer had partial responses. CONCLUSIONS: When combined with paclitaxel, the recommended dose of lonafarnib for Phase II trials is 100 mg p.o. twice daily with 175 mg/m(2) of paclitaxel i.v. every 3 weeks. Additional studies of lonafarnib in combination regimens appear warranted, particularly in patients with non-small cell lung cancer.

Adult↗
PubMed2004

Once-daily intravenous busulfan and fludarabine: clinical and pharmacokinetic results of a myeloablative, reduced-toxicity conditioning regimen for allogeneic stem cell transplantation in AML and MDS.

Postulating favorable antileukemic effect with improved safety, we used intravenous busulfan and fludarabine as conditioning therapy for allogeneic hematopoietic stem cell transplantation (HSCT) for acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS). Fludarabine 40 mg/m2 and intravenous busulfan 130 mg/m2 were given once daily for 4 days, with tacrolimus-methotrexate as graft-versus-host disease (GVHD) prophylaxis. We treated 74 patients with AML and 22 patients with MDS; patients had a median age of 45 years (range, 19-66 years). Only 20% of the patients were in first complete remission (CR) at transplantation. Donors were HLA-compatible related (n = 60) or matched unrelated (n = 36). The CR rate for 54 patients with active disease was 85%. At a median follow-up of 12 months, 1-year regimen-related and treatment-related mortalities were 1% and 3%, respectively. Two patients had reversible hepatic veno-occlusive disease. Actuarial 1-year overall survival (OS) and event-free survival (EFS) were 65% and 52% for all patients, and 81% and 75% for patients receiving transplants in CR. Recipient age and donor type did not influence OS or EFS. Median busulfan clearance was 109 mL/min/m2 and median daily area-under-the-plasma-concentration-versus-time-curve was 4871 micromol-min, with negligible interdose variability in pharmacokinetic parameters. The results suggest that intravenous busulfan-fludarabine is an efficacious, reduced-toxicity, myeloablative-conditioning regimen for patients with AML or MDS undergoing HSCT.

Adult↗
PubMed2004

Dose-finding based on efficacy-toxicity trade-offs.

We present an adaptive Bayesian method for dose-finding in phase I/II clinical trials based on trade-offs between the probabilities of treatment efficacy and toxicity. The method accommodates either trinary or bivariate binary outcomes, as well as efficacy probabilities that possibly are nonmonotone in dose. Doses are selected for successive patient cohorts based on a set of efficacy-toxicity trade-off contours that partition the two-dimensional outcome probability domain. Priors are established by solving for hyperparameters that optimize the fit of the model to elicited mean outcome probabilities. For trinary outcomes, the new algorithm is compared to the method of Thall and Russell (1998, Biometrics 54, 251-264) by application to a trial of rapid treatment for ischemic stroke. The bivariate binary outcome case is illustrated by a trial of graft-versus-host disease treatment in allogeneic bone marrow transplantation. Computer simulations show that, under a wide rage of dose-outcome scenarios, the new method has high probabilities of making correct decisions and treats most patients at doses with desirable efficacy-toxicity trade-offs.

Abciximab↗
PubMed2003

Effect of circulating blasts at time of complete remission on subsequent relapse-free survival time in newly diagnosed AML.

Standardized criteria for complete remission (CR) in acute myeloblastic leukemia (AML) require the absence of peripheral blood blasts (PBBs). However, MD Anderson (MDA) criteria for CR (CR-MDA), although including the other requirements for CR, have not included the PBB count. We exploit this difference to assess the effect of PBBs at the time of CR-MDA on relapse-free survival (RFS) time. Eighty percent of the 533 patients with newly diagnosed AML or refractory anemia with excess of blasts (RAEB) entering CR-MDA from 1995 to 2000 had no PBBs at time of CR-MDA. Ninety-three percent of the remaining patients, who thus had CR-MDA but not standard CR, had 1% to 5% PBBs at this time. Multivariate analyses, using both conventional and Bayesian approaches, indicated that PBBs had no effect on RFS. For all patients and for the subgroups given and not given granulocyte colony-stimulating factor (G-CSF), the 95% credible interval for the relative risk of failure in the PBB group was nearly centered at 1.0. Thus, our data do not support use of PBBs in defining CR in newly diagnosed AML.

Anemia, Refractory, with Excess of Blasts↗
PubMed2003

Hierarchical Bayesian approaches to phase II trials in diseases with multiple subtypes.

We propose a methodology for conducting phase II clinical trials in settings where the disease is categorized into multiple subtypes. A hierarchical Bayesian model is assumed for treatment effects within the subtypes. The hierarchical model, which is tailored to each particular application, allows treatment effects to differ across subtypes while assuming a priori that the effects are exchangeable and correlated. Two applications are described. The first is a trial of imatinib for sarcoma in which treatment activity is characterized by a binary indicator of tumour response. The second is a phase II trial of a new preparative regimen for allogeneic bone marrow transplantation in patients with haematologic malignancies, with treatment effect characterized by the mean time from transplant to disease progression or death. The applications illustrate how the hierarchical Bayesian model borrows strength across subtypes.

Antineoplastic Agents↗