Primary pulmonary malignant melanoma with H3K27Me3 loss: A case report.

Primary pulmonary malignant melanoma (pPMM) is an exceptionally rare type of primary malignant tumor. The present study reports a unique case of pPMM in a 54-year-old woman. Surgical resection revealed a tumor localized around the bronchus, showing nodular growth with relatively well-defined borders and no evidence of local or distant metastasis. To further characterize this rare pPMM, histological analysis, immunohistochemistry, sanger sequencing and next-generation sequencing were conducted. Histologically, the tumor exhibited biphasic differentiation, with both epithelial-like and spindle cell-like features, as well as high-grade characteristics, including significant atypia, necrosis and a high mitotic index. Key diagnostic features of malignant melanoma were evident, including prominent red nucleoli and melanin pigmentation. Immunohistochemistry confirmed the presence of melanoma markers and demonstrated a loss of H3K27Me3 expression. The programmed death-ligand 1 positivity rate of the tumor was 60%. NGS identified a mutation in the TP53 and NTRK3 genes, but no BRAF mutation was detected. This case report highlights the unique presentation of pPMM with H3K27Me3 loss and provides insights into its genomic profile, pathogenesis and natural history.