Serial MR in gene therapy for recurrent glioblastoma: initial experience and work in progress

To describe the MR imaging findings in a pilot study evaluating gene therapy for treatment of patients with recurrent glioblastoma.

Serial MR examinations were evaluated retrospectively in patients treated with gene therapy that included a retroviral vector containing the herpes simplex virus thymidine kinase gene and intravenous ganciclovir. Images were obtained after tumor resection and after each cycle of treatment, at approximately 40-day intervals. The volume of enhancing tissue was measured on serial MR images.

Eleven patients with recurrent glioblastoma were entered into the clinical trial of gene therapy and seven patients completed at least two cycles of treatment. Of these seven, three patients had an early (between 40 and 80 days) increase in the volume of enhancing tissue followed by a decrease or plateau in enhancing tissue volume. A fourth patient had a stable volume of enhancing tissue for 132 days. The remaining three patients had continuous increases in volume of enhancement on all subsequent MR examinations.

Although animal data show striking tumor regression in response to similar gene therapy, only limited regression was observed among the seven patients we studied. The transient increases in enhancement seen in three of seven patients might reflect an inflammatory response to local injection of the viral vector.