Unusual Magnetic Resonance Imaging Findings of a Glioblastoma Arising During Treatment with Lenvatinib for Thyroid Cancer

Background: Glioblastoma (GBM) is a lesion radiologically characterized by magnetic resonance imaging findings, such as ring enhancement with extensive perifocal edema and a butterfly appearance extending into the bilateral lobes. However, these characteristic findings could be changed by antiangiogenic therapy, with decreased contrast enhancement and improved perifocal edema. Herein, we report a case of GBM that arose during treatment with a tyrosine kinase inhibitor for another cancer. Case Description: A 57-year-old man presented with seizures. Until the seizure onset, he had been treated with the multireceptor tyrosine kinase inhibitor lenvatinib for 4 years for thyroid cancer and its metastasis to the thoracic vertebral body. Magnetic resonance imaging revealed a slightly high intensity lesion in the left frontal base area on T₂-weighted or fluid-attenuated inversion recovery images, and the lesion showed only faint enhancement on T₁-weighted images after gadolinium administration. Total resection was performed and the histopathologic diagnosis was GBM. However, grade IV histology was observed in only a limited area, and most of the specimen showed lower grade histology with moderate vascularization that lacked microvascular proliferation. Conclusions: Lenvatinib, which is antiangiogenic, might have affected the radiologic characteristics, as well as the pathology of the tumor. Brain tumors arising during treatment with receptor tyrosine kinases for other cancers could show atypical imaging findings.