An Unusual Posterior Fossa Glioblastoma Diagnosed During a Follicular Lymphoma Patient’s Follow-Up: Case Report and Review of the Literature

Introduction: Cerebellar glioblastoma (GBM) is a rare adult tumor. Precise diagnosis of cerebellar glioblastoma is important for establishing an appropriate therapeutic program. In adults with prior malignancy, cerebellar tumors are typically considered metastatic. The coexistence of cerebellar GBM with another primary cancer is extremely uncommon. Case presentation: A 72-year-old man with a history of follicular lymphoma, treated decades earlier, presented with balance issues. Brain MRI revealed a left cerebellar mass compressing the fourth ventricle. Surgical resection was performed, and pathology confirmed an IDH1-wildtype cerebellar GBM. He underwent standard Stupp protocol with radiotherapy and temozolomide. Despite second-line therapy with bevacizumab, his condition deteriorated, and he died 13 months after diagnosis. Discussion: Cerebellar GBM is aggressive and difficult to distinguish from metastasis, especially without advanced imaging. Its association with lymphoma is rare, and prior radiotherapy may be a contributing factor. The treatment remains challenging in elderly patients. Conclusion: Cerebellar GBM has a poor prognosis. When associated with other primary cancers, diagnosis and management become more complex. Histopathology is essential, but even with optimal treatment, survival is limited.