SURG-50. CLINICAL EXPERIENCE AND PATHOLOGICAL FEATURES IN AUTOPSY CASES TREATED WITH TUMOR TREATING FIELDS

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Abstract BACKGROUND Since 2017 Tumor Treating Fields (TTF) was approved for primary glioblastoma in Japan. In this study, we reviewed clinical experience and the pathological characteristics of autopsy cases treated with TTF. METHODS From March 2018 to April 2022, 67 patients (36 males and 31 females, median age 68 years) with primary glioblastoma, IDH-wild type treated at our institution were included in the analysis. RESULTS Twenty-eight patients (19 males and 9 females, median age 66 years) met the TTF indication criteria for induction, 19 cases (67.9%) were 65 years or older, and 14 cases (50.0%) indicated MGMT promoter methylation. The mean duration of TTF treatment was 7.2 months. The main reasons for discontinuation were tumor recurrence in 11 patients (40.7%), skin symptoms in 8 patients (29.6%), and psychological distress in 6 patients (22.2%). Only 12 patients (42.9%) underwent TTF treatment over 18 hours per day, because of discomfort of wearing pad and concern about srrounding. Median PFS and OS in the used patients were 9.9 and 17.7 months, respectively. Autopsies were performed in 3 of the 16 deaths. Histopathological examination of tumor specimen indicate that the Ki-67 labeling index was higher in brainstem (33.6%) than in the supratentorial primary lesion (23.6%). DISCUSSION Comparing to the previous report (Stupp R et al., JAMA. 2017), our cases contained a large number of patients over 65 years old with shorter mean duration of TTF treatment, and shorter OS. After TTF treatment, the Ki-67 labeling index was higher on infratentorial than on supratentorial in the autopsy specimens, suggesting the anti-tumor effect of TTF for the supratentorial lesion. RESULTS High proliferative activity of infratentrial lesion was suggested as a typical form of progression for TTF treatment.