Pleural Metastasis From Cutaneous Malignant Melanoma.

Abstract

Metastatic cutaneous melanoma, the incidence of which continues to increase worldwide1 is associated with a high morbidity and mortality. Although only accounting for 4% of dermatologic malignancies, it is responsible for 80% of skin cancer–related deaths.2 Common sites of metastasis include lung, liver, bone, and brain.3,4 Only 2% of melanoma patients with intrathoracic metastasis develop a malignant pleural effusion.5 It is known that elevated serum lactate dehydrogenase (LDH) can be used as an adverse prognostic factor in stage IV cutaneous melanoma.6,7 We present a case of metastatic cutaneous melanoma to the pleura in a gentleman with normal pleural fluid and serum LDH levels, a possible indicator of favorable prognosis. CASE REPORT A 76-year-old man with a past history of hypertension and cutaneous melanoma over the right arm was referred for evaluation of a pleural effusion. The melanoma was treated with local excision in January 2011 for a lesion to the right arm found to have a Breslow-thickness of 2.3 mm (T2a). Repeat excision was performed 6 months later for local recurrence in the site of the previous scar. Sentinel lymph node biopsy done at that time was negative for metastasis. Subsequent annual follow ups for the next 4 years with dermatology and oncology showed a well healed scar without local recurrence. In October 2015, the patient presented to the emergency department with complaint of abdominal pain. Computed tomography (CT) of the abdomen was performed given concern for diverticulitis, which incidentally revealed a left-sided pleural effusion with pleural thickening. Subsequent CT of the chest showed multiple pleural masses along with a large left-sided pleural effusion. A positron emission tomography/CT scan showed enhancement of the masses concerning for malignancy (Fig. 1). A thoracentesis was performed with removal of 2.5 L of hemorrhagic appearing fluid with nondiagnostic cytology.FIGURE 1: Positron emission tomography scan with increased standardized uptake of pleural masses.Medical thoracoscopy was subsequently performed which revealed numerous clusters of pink and black masses arising from the visceral and parietal pleura along with the diaphragmatic surface (Fig. A).FIGURE A: Medical thoracoscope revealed pink and black masses arising from the parietal pleura and diaphragm.Biopsies were obtained of multiple pleural-based lesions and a tunneled indwelling pleural catheter was placed. Immunohistochemical staining was positive for S100, SOX10, and Melan-A, confirming a diagnosis of metastatic cutaneous melanoma. V600 mutation within the BRAF gene was later identified. Serum and pleural fluid LDH levels were within normal range at 111 and 99 U/L, respectively. Patient was seen in the pulmonary procedure clinic after 2 weeks with decreasing pleural fluid return from the tunneled pleural catheter. Pleurodesis was confirmed with bedside pleural ultrasound and the tunneled pleural catheter was subsequently removed. He underwent treatment with Dabrafenib and Trametinib chemotherapy which resulted in complete response to therapy at 3 month-follow-up (Fig. 2).FIGURE 2: Positron emission tomography scan at 3-month follow-up with complete response to chemotherapy.DISCUSSION The incidence of metastatic cutaneous melanoma continues to rise with a global annual increase of 3% to 8%.8 With this increasing incidence comes a necessity for understanding the disease as a whole. Cutaneous melanoma is known to metastasize to the lung, however little is known about metastasis limited to the pleura given that this is an exceedingly rare event. Chen et al5 described a series of 130 patients with metastatic melanoma to the thorax, of which 3 patients (2%) had malignant pleural effusion. Patients with metastatic involvement of the lungs are categorized as stage IV M1b via the TNM staging system. This stage is labeled as an intermediate prognosis with a 53% 1-year survival rate. Metastatic involvement of the pleura alone would indicate an M1c staging of the disease. These patients carry the worst prognosis with a dismal 33% survival rate at 1 year.7 The mechanism of tumor localization to the pleura and prognosis of such patients is not known. Serum LDH has been studied as a favorable, independent prognostic indicator in stage IV melanoma and is now used as part of the staging system.9 It has been shown that 1 and 2 year survival rates are significantly improved when serum LDH is within normal limits during staging, 65% and 40%, respectively, compared with elevated serum LDH (32% and 18%) at time of staging.10 The patient presented here had normal serum and pleural fluid LDH levels at 111 and 99 U/L, respectively, at time of diagnosis. On the basis of what is known regarding serum LDH levels, the unexpected finding of normal pleural fluid LDH in this case may also serve as a favorable prognostic indicator in melanoma associated pleural effusions given this patient’s remarkable response to chemotherapy. CONCLUSIONS Metastatic cutaneous melanoma to the pleura remains exceedingly rare and ill-defined in the medical literature. Normal serum and also pleural fluid LDH may indicate favorable prognosis in this small subset of patients.