INTRODUCTION: There is limited research regarding the use of N-Acetylcysteine (NAC) to manage non-acetaminophen induced acute liver failure (NAI-ALF). NAC has an anti-inflammatory, antioxidant effect, and improves oxygenation by vasodilating microcirculation. A mortality benefit and association with lower hospitalization length has been seen when using NAC in NAI-ALF. Use of immunotherapy to treat cancer has recently increased, and acute liver injury has been reported with many agents. This case examines using NAC to manage immunotherapy induced acute liver injury (ITI-ALI). CASE DESCRIPTION/METHODS: Patient is a 67-year-old Caucasian female with a medical history of hyperlipidemia and well-differentiated angiosarcoma of the right breast, diagnosed in 2011. She had mastectomy and adjuvant chemo-radiotherapy resulting in remission. Surveillance abdominal CT, in 2017 showed new enhancing hepatic lesions. Abdominal MRI confirmed these concerning lesions. A cervical mass was noted, which was biopsied, and diagnostic of metastatic angiosarcoma. She was started on Pazopanib. Two weeks into therapy, she experienced darkened urine, myalgia, and abdominal pain. Labs just prior to admission showed transamninits, ALT of 522 units/L and AST of 456 units/L. Admission labs showed worsening transaminitis, ALT 1377 units/L and AST 1212 units/L. Exam showed jaundice and diffuse abdominal pain. Acetaminophen levels were undetectable. Abdominal ultrasound showed patent hepatic vasculature, normal liver size, appearance, echogenicity, and no intrahepatic ductal dilation or masses. Additionally, serologies for herpes simplex virus, Ebstein Barr virus, cytomegalovirus, viral hepatitis, anti-nuclear antibody, and anti-smooth muscle antibody were negative. Ultimately, her acute liver injury was suspected to be ITI-ALI. NAC was started and Pazopanib was held. Hepatic function was serially monitored, and her acute liver injury rapidly improved. She was discharged and repeat labs on follow-up continued showing improvement in transaminases (Figure 1). DISCUSSION: The use of NAC in NAI-ALF was described in a prospective study by Mumtaz, Azam, et al, and in a randomized, case-control trial by Nabi, et al. Neither studies had patients who had developed ITI-ALI. Both studies were able to conclude that using NAC in NAI-ALF reduced mortality and hospitalization length. Further prospective studies should be conducted to identify if there is a statistically significant effect on mortality and length of hospitalization by using of NAC in ITI-ALI.