Presenter: Jorge Sanchez-Garcia MD | Intermountain Medical Center Background: Surgical resection is a mainstay of treatment in intrahepatic cholangiocarcinoma (icca), but it is only possible in 10-40 % cases. In advanced disease cases, only chemo-/chemoradiotherapy is possible with a median overall survival of 11.7 months. Recent studies in precision medicine-based immunotherapy approaches have controversial results with survival improvement only in selected cases. The aim of this study is to report a case of unresectable icca treated with pembrolizumab and subsequent surgical resection. Methods: a 60-year old male presented for a second opinion for persistent abdominal pain, decreased apetite, fatigue and 3 kg weight loss. Two months ago, his diagnosis was a poorly differentiated adenocarcinoma, favour pancreaticobiliary origin (ck7, ck18, ck20 focal weak, cdx2 positive in subset in tumor cells). Due to the large size and invasive nature, palliative chemotherapy was offered but the patient refused it. In our first physical examination was notable an enlarged firm mass fixed and immovable, and a palpable liver edge. A ct scan showed large liver mass measuring 20.8x15.5 cm occupying almost all of the left liver lobe and partially the right liver lobe, other small right hepatic lobe areas were identified, the portal veins were thrombosed and the main portal vein, metastatic nodes at the aorticocaval region and minimal to moderate free fluid in the abdomen (figure 1). The patient started immunotherapy with pembrolizumab (2 mg/kg every 21 days). After the second cycle of pembrolizumab, a paracentesis removed 3.7 l of clear yellow fluid without malignant cells. Following the procedure, the patient tolerated the immunotherapy and had progressive clinical improvement. After the 16th cycle, a ct-scan showed decreased size of the liver mass (11.3x8 cm) with stable portal thrombosis. A pet-ct and mri ruled out metastatic disease. The patient underwent to open left lobectomy, open cholecystectomy, portal and pericardial lymphadenectomy and portal vein thrombectomy. Pathology reported scant viable atypical epithelial cells, prominent mucin in the liver and portal vein, and negative margins compatible with complete response, all the lymph nodes were benign. The patient was under surveillance almost two years since he started the immunotherapy and almost a year since the surgery with progression-free survival (figure 1). Results: Immunotherapy has transformed the management of a variety of advanced neoplasms. However, there are few reports of immunotherapy in icca patients and the observed therapeutic benefit has been inconsistent in this cohort. There are some case reports and keynote-028 clinical trial that have reported the outcomes of immunotherapy in biliary tract cancer, however all these studies only included patients with surgical resection, chemotherapy-refractory and progressive disease. The case reported here is the first to our knowledge of an advanced icca patient with immunotherapy as a first line of treatment who experienced a complete pathological response. Conclusion: To our knowledge, this represents the first report of neoadjuvant immunotherapy in an unresectable icca patient who experienced complete pathological response. The patient continues to have no evidence of recurrence more than 24 months after diagnosis. This study opens new horizons and opportunities in treatment and further clinical trials in personalized medicine.