Rapid Growth of a Lung Cancer Metastasis to a Pituitary Neuroendocrine Tumor: A Case Report and Literature Review.

We present an extremely rare case of lung cancer that metastasized to a gonadotroph pituitary neuroendocrine tumor, along with other organs. A 73-year-old man presented with dysarthria and bitemporal hemianopia. Head magnetic resonance imaging revealed cerebellar infarction and a pituitary tumor. Endoscopic transnasal pituitary tumor resection was performed. Pathologically, the tumor consisted of a well-differentiated neuroendocrine component, suggestive of a pituitary neuroendocrine tumor, alongside a poorly differentiated, highly malignant tumor with invasive growth. One month postoperatively, gadolinium-enhanced head magnetic resonance imaging revealed rapid growth of the residual tumor. Whole-body computed tomography and positron emission tomography revealed a 10-mm lung tumor and multiple muscle and bone metastases. Pathological examination of the pituitary tumor revealed poorly differentiated malignant cells. It was initially hypothesized that the pituitary neuroendocrine tumor had undergone malignant transformation with systemic metastases. However, further pathological examinations revealed steroidogenic factor 1-positive differentiated cells and steroidogenic factor 1-negative, synaptophysin-negative, cytokeratin-7-positive, and thyroid transcription factor-1-positive poorly differentiated malignant cells. The final diagnosis classified the tumor as a poorly differentiated lung adenocarcinoma that had metastasized to a gonadotroph pituitary neuroendocrine tumor, which showed rapid growth. Radiation and chemotherapy were administered; however, the patient died 6 months after surgery. Tumor metastasis to a pituitary neuroendocrine tumor is typically seen in older adults with non-functioning pituitary neuroendocrine tumors and no diabetes insipidus. Hence, clinicians should consider both metastatic pituitary neuroendocrine tumors and tumor metastasis to a pituitary neuroendocrine tumor when diagnosing a rapidly growing pituitary tumor in patients with signs of systemic metastasis.