1658 Colonic Metastatic Disease Masquerading as Immune Checkpoint Inhibitor-Mediated Colitis

Abstract

Listen

Translate article

INTRODUCTION: The use of immune-checkpoint inhibitors (ICIs) in the treatment of advanced cancer has increased exceptionally since ipilimumab was first approved for melanoma in 2011. As the prevalence of patients being treated with ICIs rises so too have their immune related adverse events (irAEs). Clinicians are now faced with the challenge of accurately and promptly recognizing irAEs. With immune-mediated diarrhea and colitis being two of the most common irAEs, an algorithm for their treatment has already been established; however, it is important for clinicians to maintain a broad differential diagnosis when caring for a patient on an ICI with colitis symptoms. CASE DESCRIPTION/METHODS: A 48-year-old woman with a history of metastatic, refractory, triple negative, BRCA positive breast cancer was started on pembrolizumab four years after being diagnosed with breast cancer. 18 months after initiating treatment with pembrolizumab, she developed loose, watery stools. Cross sectional imaging revealed mild, circumferential wall thickening of the proximal ascending colon. A gastrointestinal pathogen nucleic acid detection test was negative, and she was started on a two-week course of budesonide for presumed immune checkpoint inhibitor-mediated colitis (IMC). Her symptoms progressed with bright red blood per rectum and abdominal cramping. Treatment for IMC was escalated with a prednisone taper followed by infliximab infusion. 6 weeks after being treated for IMC, her hemoglobin was 7.6 and ferritin 4. She was referred to gastroenterology for iron deficiency anemia. Repeat abdominal CT revealed increased colonic wall thickening. Colonoscopy revealed an obstructing, ulcerated mass in the ascending colon. Pathology identified poorly differentiated adenocarcinoma consistent with a breast cancer metastasis. She underwent right hemicolectomy 6 months after the initial CT showed colonic thickening. DISCUSSION: Pembrolizumab is one of many ICIs that have been developed for the treatment of advanced-stage malignancies. The gastrointestinal side effects of this class of medications pose a challenge for physicians as IMC is nearly indistinguishable from many other etiologies of diarrhea clinically, and the onset of gastrointestinal symptoms ranges widely from 1 to 32 weeks after starting the medication. As the use of ICIs becomes more widespread, quick and accurate differentiation of an irAE from other life threatening pathology is of vital importance, and early colonoscopy should be considered to rule out metastatic disease.