Ghost Melanoma: Endobronchial Melanoma of Unknown Primary Mimicking Primary Lung Cancer

Melanoma of unknown primary (MUP) with endobronchial involvement is a rare diagnostic presentation that may clinically and radiologically mimic primary lung cancer. We report the case of a 46-year-old man, a chronic smoker with a 20-pack-year history and a previous excisional biopsy of an atypical scalp nevus, who presented with low-volume hemoptysis and constitutional decline evolving over three months. Chest imaging revealed a large necrotic mass involving the right middle and lower lobes, associated with bilateral pulmonary nodules in a cannonball pattern and mediastinal lymphadenopathy, initially suggesting an advanced primary lung malignancy. Bronchoscopy demonstrated an obstructing endobronchial lesion at the level of the bronchus intermedius. Histopathological examination revealed a malignant melanocytic proliferation, with immunohistochemistry showing positivity for melanoma antigen recognized by T cells 1 (Melan-A) and human melanoma black 45 (HMB-45) and negativity for thyroid transcription factor-1 (TTF-1), cytokeratin AE1/AE3 (AE1/AE3), and p40, supporting the diagnosis of malignant melanoma. Extensive evaluation for an extrathoracic primary, including complete dermatological and mucosal examination and fundoscopy, failed to identify a primary lesion. Staging revealed additional brain, peritoneal, and bone involvement at diagnosis. Primary pulmonary melanoma and MUP with endobronchial involvement were considered, with the overall clinical and pathological findings favoring the latter diagnosis. The case was discussed at a multidisciplinary tumor board, and systemic immunotherapy was initiated. This case highlights the diagnostic challenge posed by an endobronchial melanocytic lesion in a patient with a smoking history and emphasizes the importance of a thorough search for an extrathoracic primary before diagnosing primary pulmonary melanoma.