Merkel cell carcinoma (MCC), a high grade cutaneous neuroendocrine tumor (NET), is often confused with basal cell carcinoma (BCC), basaloid squamous cell carcinoma (SCC), and other primary site small cell carcinomas. Usually limited to skin and regional lymph nodes, solid organ metastasis is uncommon and results in high mortality. We present a case of a man with abdominal pain and liver lesions who was diagnosed with Merkel cell carcinoma of unknown primary (MCCUP). A 74-year-old man presented with a one-week history of shortness of breath, pleuritic chest pain, and abdominal pain. Significant medical history included prostate adenocarcinoma and Moh's surgery for SCC and BCC. On examination, he demonstrated epigastric tenderness. Laboratory studies were remarkable for elevated liver enzymes and total bilirubin. Initial workup ruled out acute coronary syndrome and pulmonary embolism; however, chest CT showed multiple pulmonary nodules and a large peri-fissural nodule. Abdominal CT showed a mottled liver and lytic lesions in the vertebral column concerning for metastasis. A liver biopsy showed high-grade NET. Immunohistochemical (IHC) staining favoring MCC and excluding primary pulmonary and gastrointestinal SCC. Hospital course was complicated by worsening jaundice and ascites for which he underwent palliative chemotherapy without improvement. Repeat imaging showed worsening hepatic metastases as well as new lytic lesions. There was a decrease in size of the peri-fissural nodule, but no change in the other lung nodules. Palliative radiation therapy was elected and the patient passed away 4 months after presentation. MCC is a rare, aggressive NET, most common in Caucasians over age 65 with UV exposure. Most patients present with cutaneous disease and regional lymph node involvement. Systemic spread is rare; however, common metastatic sites include lymph nodes, lung, liver, and bone. MCCUP typically presents with nodal disease without known primary cutaneous MCC. Histologic diagnosis of MCCUP is difficult due to similarities with more common high-grade NETs, such as pulmonary or gastrointestinal small cell carcinoma. Key electron microscopic features include dense core granules and paranuclear intermediate filaments. CK-20 positivity, and TTF-1 and CDX-2 negativity on IHC staining, to exclude pulmonary and gastrointestinal SCC, are confirmatory. Outcomes for patients with MCC is poor; treatment typically involves palliative chemotherapy.2349_A Figure 1. Computed Tomography of the Abdomen w/contrast - The liver is enlarged with a heterogeneous and mottled appearance - Axial section2349_B Figure 2. Needle biopsy of liver showing a trabecular small cell carcinoma (MCC) at 200 magnification (H&E 20X)2349_C Figure 3. Merkel cell carcinoma marking with CK20 in a para-nuclear pattern at 600 magnification (60X)