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Five years of glioblastoma multiforme (GBM) phase II trials at the radiation therapy oncology group (RTOG)
Wendy F Seiferheld, Minesh P Mehta, John Del Rowe, David MacDonald, Corey Langer, Charles Scott, Walter J Curran, W. K. Alfred Yung, American College of Radiology, Philadelphia, PA; University of Wisconsin, Madison, WI; Montefiore Medical Center, Bronx, NY; University of Western Ontario, London, ON, Canada; Fox Chase Cancer Center, Philadelphia, PA; Thomas Jefferson University, Philadelphia, PA; UT MD Anderson Cancer Center, Houston, TX.
From 1995 to 2000, the RTOG completed five phase II trials of pharmacological agents combined with standard radiation therapy(RT) for GBM. The RTOG´s development of recursive partitioning analysis (RPA) classification for GBM patients enabled a meaningful comparison of single arm trials against the RTOG GBM database of patients treated with BCNU/RT regimens. This approach facilitated the exploration of several agents via phase II trials, rather than focusing resources on a single-agent phase III trial. During this period, the RTOG enrolled 410 eligible patients onto five trials, replacing BCNU with either tirapzamine, topotecan, taxol, beta interferon, or thalidomide. Planned sample size ranged from 53 to 84 patients, as the statistical design was modified over time. None of the experimental agents from these studies demonstrated statistically significant improvement in survival from the historical control after adjusting for RPA class. On the other hand, it is important to realize that several of the studies exhibited survival similar to the historical control, and with fewer life-threatening toxicities. These results question the standard practice of concurrent BCNU for GBM patients. Furthermore, with the observed low toxicity levels, phase II testing of doublet or triplet combinations of these and other agents with RT is feasible, and may yield better results than single-agent /RT approaches.