S2071 Natural Killer Polyp

Abstract

Introduction: Natural killer (NK) cells are cytotoxic lymphocytes that can induce an innate immune response against tumors and virally-infected cells. NK cell enteropathy (NKCE) is clinically indolent although histologically it resembles NK/T-cell lymphomas.1 Therefore, accurate diagnosis is instrumental to avoid overtreatment.1 Case Description/Methods: A 45-year-old female presented with 2 episodes of nocturnal left lower quadrant “labor-like” pain lasting for 1-2 hours each, which were not alleviated by ibuprofen or acetaminophen. She described her subsequent bowel movements as bloody, skinny stool. Her pain was associated with abdominal tenderness for 3 days. She denied a change in weight or appetite but did endorse decreased energy over the last several months. Her family history is limited since she was adopted. Physical examination and lab tests were unremarkable. Colonoscopy showed a flat, 1-cm polyp with 3 erosions in the rectum. Excisional biopsy revealed polypoid fragments of rectal mucosa with atypical lymphoid infiltrate with NK cell phenotype involving predominantly the mucosa and multifocally through the muscularis mucosa (Figure 1A and 1B). Immunohistochemical staining was positive for CD3, CD7, CD56, and BCL2. Ki-67 highlighted approximately 90% of the lesional cells. These results were consistent with NKCE. The CT was unremarkable. It was decided to manage her conservatively. Repeat colonoscopy 6-months later revealed a post-polypectomy scar in the rectum (Figure 1C). Scar biopsy was negative for abnormal cells. She followed up with oncology and has been in remission for more than 5 years. Her most recent colonoscopy still showed an unchanged rectal scar. Discussion: The lack of systemic symptoms, the isolated colon location, and its EBV-negative staining point toward a diagnosis of NKCE rather than lymphoma. NKCE typically presents with vague abdominal symptoms and bleeding.1 Since NKCE mimics NK/T-cell lymphoma, it is important to accurately diagnose the disease to prevent erroneous overly aggressive treatment. Since this disease and the exact stimulus are not well established,1 further research needs to explore the appropriate standard of care for patients with NKCE.Figure 1.: A and B, histologic findings consistent with a diagnosis of natural killer cell enteropathy. C, post-polypectomy scar.