A prospective phase II study to determine the efficacy of GDC 0449 (vismodegib) in adults with recurrent medulloblastoma (MB): A Pediatric Brain Tumor Consortium study (PBTC 25B)

2035 Background: Almost 80% of adult medulloblastoma are of the SHH subtype. Second line therapy for adult MB is limited; therefore we tested the efficacy of vismodegib, a small molecule inhibitor of Smoothened (SMO) among patients with this disease. Methods: Adult patients with refractory or recurrent MB and who had measureable disease were enrolled on the study. Immunohistochemistry (IHC) was used to stratify patients to Stratum A (non-SHH group); Stratum B (SHH tumors) and Stratum C (indeterminate). All patients were treated with vismodegib at 150 mg/day PO daily. Tumor response, which had to be maintained for 8 weeks to meet protocol definition of sustained response, was assessed using RECIST criteria and central imaging review. Separate but identical Simon 2-stage MinMax designs (α = 0.10) were used in strata A and B to test for evidence that sustained response rates exceeded 5% with 90% power to detect 25% sustained response rates. Thus, 3/20 sustained responses were needed to declare potential activity of vismodegib. Results: 32 patients with a median age of 30 years (range 22.4-51.9) were enrolled on the study [Stratum A (n = 8); Stratum B (n = 20); Stratum C (n = 4)], including 18 males and 14 females. No responses were observed in Strata A or C and the median duration of treatment was 1.5 months (range 0.66-2.33). Three of 20 patients enrolled on Stratum B had sustained responses. The median duration of therapy for Stratum B patients was 2.76 months (range 0.33- 13.61). Six patients were on treatment for ≥6.44 months and 3 remain on treatment after 5.42, 9.34 and 13.61 months. During course 1, 2 patients experienced grade 3 decrease in lymphocytes; 1 experienced a grade 4 thromboembolic event; and 2 experienced grade 3 toxicities (back pain & syncope). During course 2, 3 patients experienced grade 3 toxicities (decrease in lymphocytes; myalgia & seizure). One other patient experienced grade 3 hypophosphatemia in courses 1 and 2. Conclusions: Vismodegib has activity against recurrent or refractory adult ‘SHH-subtype’ medulloblastoma and should be considered as a therapeutic option for newly diagnosed patients with this disease. Clinical trial information: NCT00939484.