Purpose: The purpose of this study was to determine the response rate of paclitaxel administered at maximal tolerated doses (MTD) in patients with newly diagnosed glioblastoma multiform.
Patients and methods: All patients in this multicenter study were 45 years or older and had measurable residual tumor on postoperative MRI scans. Up to 3 cycles of paclitaxel were administered as a continuous 96-hour intravenous infusion prior to radiation, provided that the tumor did not enlarge on serial MRIs. The initial 10 patients were treated with the previously recommended phase II dose of 140 mg/m2. Less than anticipated toxicity led to the development of a phase I/II study in 24 patients in which paclitaxel doses were escalated separately in patients receiving (+EIAED) or not receiving (-EIAED), concomitant enzyme-inducing antiepileptic drugs. Paclitaxel plasma steady-state concentrations (Css) were measured during the first cycle of chemotherapy. Response was the primary efficacy endpoint for this study, although survival was also assessed.
Results: The MTD was 140 mg/m2 in the -EIAED, and 200 mg/m2 in the +EIAED patient groups. The mean Css for the -EIAED patients treated at 140 mg/m2 was 38 nM, whereas the mean Css for +EIAED patients were 17 nm at 140 mg/m2, 27 nM at 175 mg/m2, 46 nM at 200 mg/m2, and 51 nM at 230 mg/m2. One patient, who had a verified partial response, had his diagnosis changed to an anaplastic oligodendroglioma on subsequent central neuropathologic review. None of the 15 assessable glioblastoma patients treated at or above the MTD doses showed a radiographic response to paclitaxel. The median survival of eligible patients on this protocol was 355 days (95% CI, 255 to 485 days), which is similar to the survival of comparable patients treated with conventional therapy.
Conclusions: These results suggest that (1) paclitaxel given as a 96-hour infusion at the MTD has minimal activity in patients with untreated glioblastoma, (2) the concomitant administration of EIAEDs alters the pharmacology of paclitaxel, resulting in a lower Css, reduced systemic toxicity, and higher dose requirements, (3) this study design, in which a new agent is given prior to radiation therapy (with serial monitoring of MRI), did not adversely affect survival in this patient population.