FNAB cytology of extra-cranial metastasis of glioblastoma multiforme may resemble a lung primary: a diagnostic pitfall.

backgroundAs extra-cranial metastasis of glioblastoma multiforme (GBM) is rare, it may create a diagnostic dilemma especially during interpretation of fine needle aspiration biopsy (FNAB) cytology. CASE PRESENTATION: We present transbronchial FNAB findings in a 62-year-old smoker with lung mass clinically suspicious for a lung primary. The smears of transbronchial FNAB showed groups of cells with ill-defined cell margins and cytological features overlapping with poorly differentiated non-small cell carcinoma. The tumor cells demonstrated lack of immunoreactivity for cytokeratin, thyroid transcription factor-1, and usual neuroendocrine markers, synaptophysin and chromogranin in formalin-fixed cellblock sections. However, they were immunoreactive for the other neuroendocrine immunomarker, CD56, suggesting neural nature of the cells. Further scrutiny of clinical details revealed a history of GBM, 13 months status-post surgical excision with radiation therapy and systemic chemotherapy. The tumor recurred 7 months earlier and was debulked surgically and with intra-cranial chemotherapy. Additional evaluation of tumor cells for glial fibrillary acidic protein (GFAP) immunoreactivity with clinical details resulted in final interpretation of metastatic GBM.

conclusionLack of clinical history and immunophenotyping may lead to a diagnostic pitfall with possible misinterpretation of metastatic GBM as poorly differentiated non-small cell carcinoma of lung in a smoker.