History: A 50 year old woman had polyps identified on routine colonoscopy. This polyp was resected from the rectum. What is your diagnosis?
Answer: Rectal L cell neuroendocrine tumor, Grade 1
Comment: Rectal L cell NETs are usually incidental findings on colonoscopy; they can also be identified on examination for other unrelated rectal problems. These polypoid lesions have a characteristic morphology (a): they are composed of ribbons and cords of tumor cells that form complex fingerprint-like patterns (b,c). The tumor cells stain for PSAP (d) consistent with hindgut origin. They express chromogranin (e), Peptide YY (f) and Pancreatic Polypeptide (g) and are negative for serotonin. They tend to be low grade with a Ki67 labeling index <3% (not shown) and have an excellent prognosis when completely resected.
This case was provided by Sylvia Asa, MD, PhD, a Professor of Pathology at Case Western Reserve University and an Endocrine Pathologist at University Hospitals, Cleveland Ohio. She is also the author of the Survival Guide to Endocrine Pathology, published by Innovative Science Press. You can order your copy at: