P1791 - An Interesting Rare Case of Mixed Neuroendocrine Non-Neuroendocrine (MiNEN) Rectal Tumor

Anne Jarvis, MD¹, Paresh M. Sojitra, MD², Savio Reddymasu, MD^1
1Creighton University, Phoenix, AZ; ²Creighton University, Chandler, AZ

Introduction: Mixed Neuroendocrine Non-neuroendocrine (MiNEN) tumors are a subgroup of gastroenteropancreatic neuroendocrine tumors (GEP-NET), which represent the second most common digestive tract cancers in terms of prevalence. Of all colorectal tumors, MiNEN are uncommon with low prevalence and commonly diagnosed in advanced stages. Diagnosis of MiNEN is difficult, and detailed observation of histopathology is important for diagnosis. We present a case of MiNEN rectal tumor for increased awareness of this rare diagnosis.

Case Description/Methods: 75-year-old man with history of prostate cancer status post radiation presented for endoscopic evaluation of rectal lesion. He underwent flexible sigmoidoscopy and rectal Endoscopic ultrasound and was found to have a 3 cm laterally spreading tumor in the distal rectum occupying about 75% of the rectal circumference. He underwent endoscopic mucosal resection with histology showing combined invasive moderately differentiated adenocarcinoma and high-grade neuroendocrine carcinoma consistent with mixed neuroendocrine and non-neuroendocrine neoplasm (MiNEN). On repeat flex sigmoidoscopy, a 6 mm nodule in the distal rectum was removed using Ovesco full-thickness resection device with benign pathology.

Discussion: Neoplasms displaying coexistence of neuroendocrine and non-neuroendocrine histology have been described in almost all organs. Two components of these mixed neoplasms can exhibit variable morphological features as well as degrees of differentiation and can be classified based on different cellular patterns seen on histology - collision, composite or amphicrine tumors. Besides their histological heterogeneity, over the years, mixed neuroendocrine-non-neuroendocrine neoplasms have been classified under different definitions giving rise to an inconsistency in published data. Due to these inconsistencies, literature regarding their epidemiology, biology, and management is conflicting. In the absence of clinical trials, MiNENs are commonly treated according to the standard of care for pure neuroendocrine carcinomas or adenocarcinomas from the same sites of origin, based on the assumption of a biological similarity to their pure counterparts. Due to limitations in diagnostic methods, the incidence of MiNENs may be underestimated and so we report this case to add to the literature so that future efforts might be taken to explore possible biological similarities between these tumors’ components as well as to identify potential targets for novel therapeutic approaches.



Disclosures:


Anne Jarvis, MD¹, Paresh M. Sojitra, MD², Savio Reddymasu, MD¹. P1791 - An Interesting Rare Case of Mixed Neuroendocrine Non-Neuroendocrine (MiNEN) Rectal Tumor, ACG 2023 Annual Scientific Meeting Abstracts. Vancouver, BC, Canada: American College of Gastroenterology.