INTRODUCTION: Primary Sclerosing Cholangitis (PSC) presents with hepatic duct inflammation, fibrosis and stricturing leading to biliary obstruction, recurrent cholangitis and eventually end-stage liver disease. There is a strong association between PSC and Inflammatory Bowel Disease (IBD), especially Ulcerative Colitis (UC), which itself is strongly associated with Colorectal Cancer (CRC) development. Thus, all patients diagnosed with PSC must undergo a colonoscopy to evaluate for concomitant IBD even if asymptomatic at the time of diagnosis. The cumulative absolute risk of CRC or dysplasia in patients with both PSC and UC is approximately 5 to 6 times higher than CRC in UC alone. The classic presentation of PSC is marked by abnormal liver enzymes or cholestatic symptoms. Subsequent colonoscopy identifies underlying IBD in up to 80% of cases which often progresses to CRC. We describe the case of a healthy 29-year-old male newly diagnosed with PSC. Colonoscopy revealed an extremely rare presentation of adenocarcinoma without apparent underlying IBD. CASE DESCRIPTION/METHODS: 29-year-old active-duty male presented with 6 days of nausea, vomiting, scleral icterus and abdominal discomfort. Initial total bilirubin was 11.7 mg/dL with transaminitis, elevated alkaline phosphatase and CA 19-9. IBD panel and infectious workup were negative. RUQUS and abdominal CT revealed segmental dilatation of common bile duct and mural thickening of the sigmoid colon. Follow-up MRCP / ERCP showed severely stenotic main bile duct limiting further evaluation (Figure 1). Colonoscopy found a hemicircumferential, ulcerated, friable 4 cm × 3 cm mass in the sigmoid colon, with otherwise normal colonic mucosa (Figure 2). Histologic examination demonstrated invasive poorly differentiated adenocarcinoma. His bilirubin continued to rise to 19.4 mg/dL and required biliary drain placement. Subsequent CT chest showed multiple scattered, solid nodules and the patient was transferred for further staging and potential liver transplant. DISCUSSION: This case is notable as our patient’s PSC diagnosis was immediately followed by the discovery of colon adenocarcinoma without underlying IBD. Though IBD in patients with PSC tends to be asymptomatic at the time of diagnosis, the endoscopic and histologic appearance of the colon is nearly always consistent with underlying IBD. This case exemplifies that PSC may be a direct risk factor for the development of CRC even in the absence of underlying IBD.Figure 1.: ERCP with limited contrast transmission (arrow) due to the severely stenosed main bile duct.Figure 2.: Fungating Sigmoid Colon lesion prior to biopsy.