Central pathology review in clinical trials for patients with malignant glioma. A report of radiation therapy oncology group 83-02

BACKGROUND: Confounding biologic factors, including histologic grade, may influence the outcome of adult patients with malignant gliomas more than may modifications in therapeutic approach. Any clinical trial design for malignant gliomas in adults must account for such biologic factors, including the accurate identification of the two histologic subgroups astrocytoma with anaplastic foci (AAF) or glioblastoma multiforme (GBM), which are associated with distinctly different survival outcomes. This paper examines the need for a central pathology review before entry of patients in cooperative group clinical trials stratified by histologic grade. METHODS: Pathology slides from Radiation Therapy Oncology Group (RTOG) trial 83-02, a randomized Phase II study of hyperfractionated and accelerated hyperfractionated radiation therapy and carmustine for malignant gliomas, provided 747 analyzable cases, with 680 (91%) available for central pathology review. This review was performed by a single pathologist according to RTOG/Eastern Cooperative Oncology Group histopathologic criteria. The kappa statistic was used to measure agreement between the institutional and central classification of AAF and GBM. The influence of misclassification was examined using computer simulation of varying clinical trial sizes (n = 25, 50, or 200). The effect on the statistical power of trials (n = 200) with varying mixtures of AAF and GBM tumors was investigated using computer simulations. RESULTS: Of 159 tumors classified as AAF by institutional pathology review, only 66% (105) were classified as AAF (AAF/AAF) by central review, and 54 of these cases (34%) were classified as GBM (GBM/AAF), whereas 96% (501) of 521 institutionally classified as GBM (GBM/GBM) were similarly classified by central review. Computer simulations demonstrated a 59% underestimation in the median survival (1.82 vs. 4.49 years) for trials of patients with institutionally defined AAF compared to patients with centrally defined AAF in studies of 200 patients, resulting from the addition of poor prognosis of GBM in the trial. Misclassification can also substantially reduce the statistical power of a clinical trial. In one of the simulation studies, statistical power was reduced from 65% to 14% if 50% of the patients were to receive an inaccurate histologic classification. Even greater losses in power are possible in many plausible clinical settings. CONCLUSIONS: This examination of a central versus an institutional pathology review demonstrates a low level of agreement on AAF classification and a high level of concordance on GBM classification. The results indicate the need to adjust sample size for trials of both AAF and GBM tumors to have adequate statistical power. A central pathology review remains essential for trial entry for patients with AAF and could be omitted for trials enrolling patients with GBM only.