P11.63.B Thrombocytopenia limits the feasibility of salvage lomustine chemotherapy in recurrent glioblastoma: a secondary analysis of EORTC 26101

Abstract

Abstract Background Chemotherapies used for the treatment of primary brain tumors frequently induce hematological toxicity. Thrombocytopenia represents the main cause of stopping chemotherapy for toxicity. Here we explored the incidence, and the consequences for treatment exposure and survival, of thrombocytopenia induced by lomustine chemotherapy at first recurrence of glioblastoma. Methods We performed a retrospective analysis of thrombocytopenia at first recurrence of glioblastoma, its consequences for treatment delivery, and associations with outcome in the phase II and III parts of EORTC 26101, a randomized trial designed to define the role of lomustine versus bevacizumab versus their combination in glioblastoma patients at first relapse. Results 225 patients were treated with lomustine alone (median 1 cycle) (group 1) and 283 patients were treated with lomustine plus bevacizumab (median 3 lomustine cycles) (group 2). Among cycle delays and dose reductions of lomustine for toxicity, thrombocytopenia was the leading cause. Among 129 patients of group 1 and 187 patients of group 2 experiencing at least one episode of thrombocytopenia, 36 patients in group 1 and 93 in group 2 had their treatment modified because of thrombocytopenia. Lomustine was discontinued for thrombocytopenia in 16 patients (7.1%) in group 1 and in 38 patients (13.4%) in group 2. Patients with O6-methylguanine DNA methyltransferase (MGMT) promoter-methylated glioblastoma treated with lomustine alone experienced more interference with study treatment than patients with tumors without MGMT promoter methylation. On adjusted analysis accounting for major prognostic factors, treatment modification by thrombocytopenia was a positive prognostic factor for overall survival, and this effect was entirely driven by patients with tumors without MGMT promoter methylation only. Conversely, thrombocytopenia was associated with inferior progression-free survival in patients with MGMT promoter-methylated tumors, suggesting a link to insufficient lomustine exposure. Conclusion Drug-induced thrombocytopenia is a major limitation to adequate exposure to lomustine salvage chemotherapy in patients with recurrent glioblastoma. Its association with survival suggests that mitigating thrombocytopenia to allow enhanced drug exposure in patients with MGMT promoter methylated tumors might improve outcome.