INTRODUCTION: Primary malignant melanoma of the lung (PMML) is an exceedingly rare and highly aggressive neoplasm.
CASE PRESENTATION: A 27 year old man was referred to the pulmonary clinic for evaluation of a large right lower lobe mass discovered on a chest xray performed because of scant hemoptysis. He had smoked 5 cigarettes daily for the preceding 10 years. The patient was a thin Caucasian male with a fair complexion. There were diminished breath sounds over the lower right hemithorax. There was no lymphadenopathy. The testicular exam was normal. There were no suspicious appearing nevi or other skin lesions. A CT scan of the chest with intravenous contrast demonstrated a heterogeneously-enhancing mass in the right lower lobe that measured 10.4 by 5.8 cm in its greatest transaxial dimensions. A solitary 2.1 X 1.7 cm right hilar lymph node was also present. The mass and lymph node were hypermetabolic on a whole-body PET scan. A brain MRI was normal. Bronchoscopy revealed an endobronchial lesion extending out of the right lower lobe superior segment and transbronchial biopsy specimens were obtained. Two weeks later, he underwent thoracotomy and right lower lobectomy. Diffuse sheets of malignant cells with characteristic cytoplasmic melanin production were present in both the transbronchial lung biopsy and lobectomy specimens. Immunohistochemical staining was positive for S-100 and HMB-45 markers and negative for keratin which strongly supported the diagnosis of melanoma.
DISCUSSION: Distinguishing PMML from the much more common melanoma metastatic to the lung is difficult. Twenty percent of melanoma lung metastases present as a solitary pulmonary nodule.1 To ensure proper classification, clinical criteria for the diagnosis of PMML have been proposed3. These criteria are widely accepted1,2 and should include the following: 1. A solitary lung mass or nodule 2. Typical histopathology confirmed by immunohistochemistry and/or electron microscopy 3. No prior history of melanoma or excision/fulguration of a cutaneous, mucous membrane, or ocular lesion unless the pathologic examination ruled out a melanoma 4. No demonstrable tumor elsewhere at the time of diagnosis. Our case fulfilled each of these criteria. A thorough search for other possible sites of a primary melanoma lesion included a dilated ophthalmic exam performed by an ophthalmologist and a detailed inspection of the skin and nails by a dermatologist. There were no lesions suspicious for melanoma, nor signs of a regressed melanoma. Finally, the whole body PET/CT showed no evidence of malignancy elsewhere at the time of diagnosis. The prognosis of PMML is poor and a majority of patients die of metastatic disease ( median 14 months after resection ).1 According to a recent review, only 30 cases of PMML have been reported in the English literature. Of these, 25 had surgical resection and only eight were free of disease at the time they were reported ( range 18 months to 11 years ).2
CONCLUSIONS: One month after thoracotomy and right lower lobectomy showing clear tissue margins, the patient developed recurrent hemoptysis. A new 1.5 cm mass in the posterior oropharynx proved to be melanoma by biopsy. A PET/CT also showed new adrenal and small bowel metastases. None of these lesions had been present on the PET or CT scan performed just 6 weeks earlier. A repeat brain MRI showed a new lesion in the right parietal lobe. He died 4 ½ months after diagnosis.
Reference #1 Wilson RW and Moran CA. Primary melanoma of the lung: a clinicopathologic and immunohistochemical study of eight cases. Am J Surg Pathol 1997; 21:1196-1202.
Reference #2 Maeda R, Isowa N, Onuma H, et al. Primary malignant melanoma of the lung with rapid progression. Gen Thorac Cardiovasc Surg 2009; 57:671-674
Reference #3 Jensen OA and Egedorf J. Primary malignant melanoma of the lung. Scand J Respir Dis 1967; 48:127-135.
DISCLOSURE: The following authors have nothing to disclose: Steven Praske, David Bradshaw, John Roberts, John Childs
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