P14.58 Efficacy and safety of lomustine versus fotemustine as first and second line treament in relapsed glioblastoma patients

BACKGROUND Glioblastoma (GB) is the most aggressive primary brain tumour. Despite the survival benefit associated with adjuvant therapy, most of patients (pts) relapse after initial therapy. Nitrosoureas (NU) are the standard treatment at relapse in Europe. Both fotemustine (FM) (Addeo schema) and lomustine (LM) (administered orally every 6 weeks) are used in this context. MATERIAL AND METHODS This retrospective cohort study included pts diagnosed with GB treated with NU at relapse in four Catalonia hospitals from 2010 to 2020. Clinical and pathological data were collected from medical records. We analysed 6months-progression-free survival (6m-PFS), progression-free survival (PFS) and overall survival (OS) from the start of NU to progression or death respectively. Differences in toxicity grade using CTCAE v5.0 were analysed globally as ‘non-toxicity’, ‘mild toxicity (grade 1 or 2)’ and ‘high toxicity (grade 3 or 4)’. RESULTS We identified 236 GB pts with a median age of 58 years old. 29% of the pts presented MGMT promotor methylation and only 3%(n=7) had IDH mutation. After a median follow-up of 20 months, 94% of the pts were dead at the time of the analyses. At first line, 83 pts were treated with FM and 18 with LM. Pts treated with FM had better performance status (PS) than those treated with LM (p=.010). Median PFS was 2 months and 6m-PFS was 12% vs 6% in FM and LM group respectively (p=.87). Median OS was 3 months with LM vs 6 months with FM, with no statistically significant differences even adjusted for prognostic factors (p=.79 HR:0.9 CI 95% 0.41–1.96).At second line, 78 were treated with FM and 24 with LM, no differences between groups. Median PFS was 2 months in both groups and median OS was 3 vs 5 months for pts treated with LM vs FM respectively, with no significant differences. 6m-PFS was 13% for LM vs 0% for the FM group (p=.39).Pts received a mean of 1.7 cycles (every 6 weeks) and 4.1 cycles (every 2 weeks) in LM and FM group, respectively. Thrombocytopenia was the most common serious side-effect, with a higher proportion of grade 1–2 toxicity in the FM group (p=.03) that also required more treatment delays (p=.01). CONCLUSION Despite being retrospective study and a few pts were treated with LM, there were no differences neither in PFS nor in OS in pts treated with LM vs FM at first or second line. Higher G1-2 thrombocytopenia was shown in the FM group probably due to a higher number of hematology samples collected.