C59-12 Rare Presentation of Primary Malignant Melanoma of the Lung in a Mountain Climber: A Case Report

Abstract Primary malignant melanoma of the lung (PMML) is an exceptionally uncommon entity, comprising approximately 0.01% of all primary lung tumors and 0.4% of all melanomas overall. Melanoma is a histological diagnosis but immunohistochemical staining is often required to confirm spindle cell origin. Most melanoma cases involving the respiratory system represent metastatic disease from cutaneous or mucosal primaries, further highlighting the rarity of PMML. A 66-year-old professional mountaineer with no significant past history presented with complaints of low back pain with tingling in the lower limbs. On physical examination, there was localized tenderness. Despite symptomatic treatment, symptoms persisted. Two months later, the patient returned with new-onset rib pain. Spinal imaging demonstrated metastatic lesions in the T1 and T11 vertebral bodies. A PET-CT confirmed a primary lung malignancy with metastases to the vertebra and liver. A CT chest identified a spiculated mass in the left upper lobe. CT-guided biopsy of the left upper lobe mass revealed a diagnosis of spindle cell melanoma, a rare subtype, with BRAF wild-type status and confirmed bone metastases. Immunohistochemistry showed a tumor proportion score of 1%. Molecular profiling demonstrated negative BRAF, NRAS, and KIT mutations, microsatellite stability, a tumor mutational burden in the 99th percentile, and a TERT promoter mutation. The patient received palliative radiation therapy and was started on combined immune checkpoint blockade along with denosumab for bone metastases. While melanoma predominantly arises from cutaneous melanocytes due to ultraviolet (UV) radiation exposure, melanoma can also occur in other sites. One of the rarest presentations is PMML. Although no specific data links PMML to mountain climbers, some studies suggest that increased UV exposure at higher altitudes may contribute to the overall risk. The treatment of PMML is not standardized due to its extreme rarity. Current therapeutic strategies are largely from protocols used for cutaneous and mucosal melanomas. Surgical resection remains the cornerstone of treatment. In metastatic disease, immunotherapy emerged as a frontline approach, although there are no definitive treatment options, making it an interesting topic for future research. This abstract is funded by: none