Primary malignant melanoma of the lung with rapid progression

This report presents a case of primary malignant melanoma of the lung with rapid progression in a 68-year-old man. During a regular checkup, a chest roentgenogram revealed an abnormal shadow in the left lower lung field. Computed tomography (CT) of the chest revealed an ill-defined tumor shadow measuring 4 x 3 cm in the left upper lobe. A CT-guided lung biopsy suggested a large-cell carcinoma, and left upper lobectomy was performed. Histopathologically, the tumor was comprised of malignant epithelial tumor cells with large amounts of acidophilic cytoplasm and prominent nuclei. A dark brown pigment was observed in the tumor cells. Immunohistochemical staining was positive for S-100 protein and HMB45; staining for cytokeratin, CAM5.2, and chromogranin was negative. The final diagnosis was malignant melanoma of the lung. Two months later, multiple brain metastases developed, and he died of the disease 6 months after the surgery.