Well-Differentiated Neuroendocrine Tumor Emerging Following Chemoradiation Therapy of a Colorectal Adenocarcinoma

Abstract

Neoadjuvant chemoradiation is one of the cornerstones of colorectal adenocarcinoma management. This approach can lead to tumor regression in some patients and has shown to be prognostically beneficial. We report a case of rectal neuroendocrine tumor occurring following chemoradiation of a rectal adenocarcinoma. The patient is a 45-year-old man of Asian descent who was found to have a moderately differentiated nonmucinous adenocarcinoma of the rectum during a rectal bleeding work-up, for which he received chemoradiation prior to resection. The resection specimen showed an ulcerating lesion in the rectum at the site of previous adenocarcinoma. Microscopic evaluation revealed nests of well-differentiated neuroendocrine cells. Immunohistochemistry for AE1/AE3, synaptophysin, chromogranin A, S100, melan-A, HMB45, RCC, PSMA, PSAP, CD68, and Ki67 was performed. No histopathologic evidence of residual adenocarcinoma was present in the resection specimen at the location of the original biopsy, indicative of tumor regression. However, a well-differentiated (G1) neuroendocrine tumor was found at this same site. The tumor stained with AE1/AE3 and synaptophysin, and was negative for all other stains. Only 5 similar cases have been reported in the literature, in one case series, which have shown neuroendocrine tumors developing in the context of complete or partial regression of primary rectal adenocarcinoma following chemoradiation. Several case series have shown increased numbers of neuroendocrine cells in post chemoradiationtreated rectal adenocarcinomas. Further study is needed to establish the association between chemoradiation and the development of increased neuroendocrine cells and neuroendocrine tumors in the rectum.