Effects of re-challenge with temozolomide in grade 2/3 IDH mutant gliomas at first progression.

Background: Patients with WHO grade 2 and 3 isocitrate dehydrogenase mutation (IDHmt) gliomas commonly receive temozolomide (TMZ), with or without radiation therapy, as initial therapy. At progression, TMZ is sometimes reinstated despite a paucity of data on effectiveness.

Methods: We reviewed imaging outcomes of patients with WHO 2016 grade II/III IDHmt gliomas re-treated with TMZ at first progression between 2007 and 2019. Tumor growth rates were calculated over the year preceding re-treatment and throughout the re-treatment period, ranging from 3 to 41 months. RANO criteria were utilized to assess TMZ response rate.

Results: 15 subjects included six grade II, five grade III oligodendrogliomas, one grade II and three grade III astrocytomas. Median time between completion of the first TMZ course and initiation of re-treatment was 47 months. Median progression-free survival with TMZ re-treatment was 27.4 months and median overall survival was 47.8 months. Mean rate of tumor growth by bidimensional product increased from 0.29 cm² /month, in the year prior to first tumor progression, to 0.47 cm²/month during re-treatment, ranging from 3 to 41 months, with monotherapy TMZ. Volumetric mean rate of tumor growth was 1.12 cc/month in the year prior to first tumor progression versus 1.29 cc/month during TMZ re-treatment. Five patients experienced tumor growth rate reduction, of whom 3 patients experienced tumor shrinkage as measured by 2D; 2 of these 3 patients also experienced tumor shrinkage as measured by 3D. There was no radiographic response by RANO criteria.

Conclusion: These findings suggest previously treated, progressive IDHmt gliomas are generally resistant to TMZ, underscoring the need for alternative approaches.