Pulmonary Adenocarcinoma Metastasising to Mandibular Gingiva: Diagnostic Insights

Background Oral metastases from lung cancer are exceedingly rare and often mimic primary oral lesions, posing significant diagnostic challenges. Case Presentation We report a patient under oncological care for pulmonary adenocarcinoma who developed a rapidly enlarging 3‐cm mandibular gingival mass. An incisional biopsy was performed to investigate suspected malignancy. Histopathological analysis revealed a poorly differentiated, infiltrative epithelial neoplasm. Immunohistochemistry demonstrated diffuse positivity for cytokeratin (AE1/AE3) and strong nuclear expression of thyroid transcription factor‐1 (TTF‐1). Negative markers, including p63, CD45, PAX8, and S100, successfully excluded primary oral squamous cell carcinoma and other mimics, confirming metastatic pulmonary adenocarcinoma. The patient received palliative care but deteriorated rapidly. Conclusion Metastatic lung cancer must be considered in the differential diagnosis of atypical gingival lesions. Prompt biopsy combined with targeted immunohistochemistry, particularly TTF‐1, is essential for accurate diagnosis and guiding appropriate palliative management.