Metastatic Endometrial Cancer to the Sigmoid Colon Masquerading as Primary Colorectal Cancer.

A 67-year-old female presented with a chief complaint of hematochezia. Medical history was notable for stage 1a endometrial carcinoma status post treatment with radiotherapy alone. The patient was not considered a candidate for surgical intervention at the time due to multiple underlying comorbidities. Colonoscopy revealed a 4 cm, nonobstructive, friable, and ulcerated mass in the sigmoid colon. Initially this was concerning for a primary colorectal carcinoma, although immunohistochemistry revealed a uterine endometrial origin of the lesion. A total hysterectomy was eventually performed along with surgical resection of the affected segment of the colon, which was followed by radiation therapy. This case illustrates an unusual site of metastasis for endometrial carcinoma. The colonic metastasis of endometrial adenocarcinoma is reported to be rare and unusual, especially in the absence of endometriosis. Immunohistochemistry staining is an important adjunct in distinguishing the diagnosis of endometrial adenocarcinoma from primary colorectal carcinomas. Primary colon cancers are cytokeratin-7 negative and cytokeratin-20 positive, whereas endometrial cancers are cytokeratin-7 positive and cytokeratin-20 negative. This case is important given the scarcity and peculiarity of metastatic colon cancer originating from uterine adenocarcinomas. The possibility of metastatic disease should be maintained with identification of solitary colonic lesions, especially when there is a prior history of malignancy.