A case of primary malignant melanoma of the lung

Abstract

Background : Primary malignant melanomas of the lung are very rare, constituting only about 0.01% of all lung tumors.
Case : An abnormal shadow on the lung of a 46-year-old woman was detected on a chest X-ray. A CT scan showed a nodule measuring about 3 cm in her left lower lobe. With bronchoscopy we found a polypoid lesion in the left B8, and performed a cytological and tissue biopsy. Cytological examination revealed atypical cells as loose clusters or scattered single cells. We found brown granules in the background. Enlarged cleaved nuclei were eccentrically located. Increased amounts of nuclear chromatin demonstrated fine or coarse granules. Nucleoli were prominent. We found nuclear inclusion bodies. The abundant cytoplasm was weakly cyanophilic and contained brown-colored granules. Pathological examination showed round or spindle shaped atypical cells. The tumor cells had irregular-shaped nuclei and abundant eosinophilic cytoplasm, containing brown to black pigment. On immunohistochemistry, tumor cells were positive for HMB-45, Melan-A and S-100, but were negative for TTF-1. Because extensive examination outside the lung revealed no primary tumor, we diagnosed this case as a primary malignant melanoma of the lung.
Conclusion : Brown pigment in cytology specimens may suggest a diagnosis of malignant melanoma of the lung.