Abstract
BACKGROUND: Tumor treating fields (TTFields) treatment has been an important option for the treatment of glioblastoma. The introduction of novel treatment options may lead to distinct recurrence patterns compared to those observed with conventional therapies; however, the specific recurrence pattern during TTFields treatment has not been elucidated. METHODS AND RESULTS: Here, we analyzed 39 cases of glioblastoma treated with TTFields. Although a usage rate of more than 75% is recommended, among 39 cases, 18 discontinued TTFields treatment owing to requests by patients with lower usage rates. In these discontinued cases, patients exhibiting sensory aphasia were more frequently included compared to those who continued TTFields (44.4%, p < 0.001). Among 21 cases involving patients who continued TTFields, tumor recurrence was observed in 15 of those cases. Five out of 15 cases (33.3%) exhibited recurrence in distant parenchyma from the primary lesion. A higher usage rate and relatively longer use of TTFields were observed in these five cases, along with more favorable progression-free survival than those in the other 10 cases (p = 0.019, p = 0.040, and p = 0.024, respectively). In one case, recurrent tumors with lower grade glioma histology but molecular markers characteristic for glioblastoma, IDH-wildtype were indentified. This tumor arose in an area that received a lower local minimum power density of TTFields compared to the primary lesion, following long-term TTFields therapy. CONCLUSIONS: Long-term use of TTFields might be correlated with a high frequency of distant parenchymal recurrence in cases with favorable response.