Secondary Gastrointestinal Melanoma of Unclear Origin

Abstract

Metastatic melanoma has a predilection for the lungs, bones, GI tract, and brain. Overall, the incidence of GI organ metastases in metastatic melanoma is 43%, with the liver being the most common (58.3% of cases). The stomach is a much rarer GI destination: 7th overall after liver, peritoneum, pancreas, small bowel, spleen, and colon. An 89 y.o. male with past medical history significant for atrial fibrillation and COPD presented with difficulty swallowing. He had been having increasing dysphagia to solids over the past year and was now unable to swallow liquids. He admitted to 20-pound weight loss over the preceding year. Patient had a smoking history though he quit in 1946. Previous esophagogastroduodenoscopy a week prior to admission showed esophageal narrowing for which received Botox injections for suspected achalasia. On admission, the patient was hemodynamically stable though appeared malnourished. Labs were unremarkable. A contrast enhanced CT thorax showed a 7.5cm mass at the gastroesophageal junction (GEJ). [Fig. 1.] He underwent endoscopic ultrasound which showed a lobulated mass just below GEJ measuring 68 x 55 mm. [Fig. 2]. Biopsy showed an epithelioid/ spindle malignant tumor consistent with metastatic melanoma. [Fig. 3] The patient was deemed to be a poor surgical candidate and instead had a percutaneous endoscopic gastrostomy tube placed with plans for palliative chemotherapy. No primary lesion was identified.2627_A Figure 1. CT Thorax w/ contrast showing the 7.5cm mass at the GE Junction (between red arrows).2627_B Figure 2. Mass abutting gastric wall on EUS.2627_C Figure 3. Fine needle aspiration of the perigastric mass displays cellular smears composed of sheets or clusters of atypical epithelioid cells (A) along with scattered loosely cohesive epithelioid to spindle cells. By immunohistochemistry, the neoplastic cells are positive for melanoma cocktail (B), S100 protein (C) and SOX10 (D) while exhibiting no immunoreactivity with CD117, DOG-1, CD45, CD3, CD20, desmin, pan-cytokeratin (AE1/AE3), chromogranin and CD99. The morphologic and immunohistochemical features are most consistent with metastatic melanoma.The prognosis of metastatic melanoma is poor, with a mean survival of only 6-8 months and a 5-year survival rates less than 10%. Outcomes also depend on the site of metastases, with worse survival rates in those with metastases to visceral organs, particularly the GI tract. Treatment of metastatic melanoma of the GI tract include surgical resection, immunotherapy, and biochemotherapy. Mean survival for curative resection is 48.9 months, 5.4 months for palliative procedures, and 5.7 months for non-surgical interventions. As in this case, 4-10% of metastatic melanomas present with occult primary lesion. Theories on mechanism include the primary lesion undergoing complete regression or, falling under detection threshold. Histopathologic regression within melanoma has been reported to be 6 times that of other cancers.