Bladder Metastasis From Lung Adenocarcinoma: A Rare Case.

Bladder metastasis from primary lung adenocarcinoma is an infrequent clinical entity. Due to its rarity and nonspecific presentation, it is often misdiagnosed as primary urothelial carcinoma. We report the case of a 65-year-old male with a history of metastatic lung adenocarcinoma presenting to the emergency room with sudden gross hematuria. Imaging revealed a new bladder lesion. Following transurethral resection, histopathological and immunohistochemical analysis confirmed metastatic lung adenocarcinoma (thyroid transcription factor-1-positive/cytokeratin 7-positive/cytokeratin 20 negative/GATA binding protein 3-negative or TTF-1+/CK7+/CK20-/GATA3-). The case was discussed at the Genitourinary Oncology Tumor Board, and given the prognosis of metastatic lung adenocarcinoma, the patient opted for palliative care. This case highlights the importance of considering metastatic spread to the urinary bladder in patients with advanced malignancy who develop new urinary symptoms. Accurate diagnosis through histopathology and immunohistochemistry is essential for guiding appropriate management.