Primary Malignant Melanoma of the Lung (PMML): A Case Series

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Conference Proceeding

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INTRODUCTION: Malignant melanoma of the lung is nearly always metastatic in origin, and primary tumors are extremely rare. Up until 2017, only 40 such cases had been reported in the medical literature. Herein, we report two cases of primary malignant melanoma of the lung (PMML), which were diagnosed by excluding any extra-pulmonary origin using both a PET scan and dermatologic evaluation. CASE PRESENTATION: The first case describes a 65-year-old male with a history of basal cell carcinoma and a family history of lung CA [mother]. He's a lifelong nonsmoker and works as a manual laborer. On routine evaluation, a chest X-ray revealed right lower lobe (RLL) parenchymal changes. A follow-up chest CT showed RLL 1.8cm x 1.7cm non-calcified, speculated nodule adjacent to the major fissure with an associated 1.1cm right hilar lymph node. PET subsequently revealed the lesion was FDG avid. No other lesions or areas of uptake were noted, suggesting the lung was the primary organ of involvement. Bronchoscopy with EBUS-FNA revealed a positive right hilar node showing a sparse cellular specimen containing dis-cohesive large malignant cells in a background of small lymphocytes. Further histopathologic evaluation showed SOX10 and S100 positivity with negative staining for cytokeratin Ae1/3. The pathologic diagnosis was consistent with malignant melanoma. No cutaneous or mucosal lesions were identified, and further brain imaging was negative. He was treated surgically followed by postoperative immunotherapy.The second case is a 79-year-old male with a history of prostate cancer in remission. He endorses a two-packyear smoking history and denies significant occupational exposure. He was incidentally found to have two sub-centimeter pulmonary nodules in the right middle lobe (RML). Follow up CT chest revealed a new 2cm lung nodule in the RLL and stable two sub-centimeter nodules in the RML. Whole body PET showed an FDG avid nodule in the RLL and no other areas of involvement. Subsequent CT guided biopsy revealed malignant melanoma. The immunohistochemical profile showed S100 protein and HMB-45 positivity with negative epithelial or mesenchymal staining. Dermatologic and ophthalmologic evaluation revealed no suspicious lesions. Surgical resection was performed with histopathology confirming the diagnosis. A follow-up PET scan showed stable lung nodules without FDG activity. DISCUSSION: A diagnosis of PMML is based on a combination of clinical and pathological criteria. The clinical criteria center around the presence of a solitary lung mass or nodule in the absence of history suggestive of a previous melanoma or a melanoma outside the thorax at the time of surgery. The established pathological criteria incorporate pathognomonic immunohistochemical staining for S-100 and HMB-45, evidence of junctional change with nesting of melanoma cells or spindle cells arranged in fascicles, and invasion of bronchial epithelium in an area without epithelial ulceration. Indeed, other melanotic tumors should be excluded before reaching the diagnosis. In both of the aforementioned patients, tumor cells expressed HMB45, S-100, and MART1, whereas they did not express EMA or cytokeratin, allowing for a confident diagnosis. CONCLUSIONS: PMML is cited as the rarest type of visceral melanoma. Accurate diagnosis requires detailed investigation and fulfillment of specific criteria




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Chest Annual Meeting 2023, October 8-11, 2023, Honolulu, HI

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