Endometrioid Adenocarcinoma With Solitary Metastasis to the Appendix, Mimicking Primary Appendiceal Adenocarcinoma: A Case Report and Literature Review.

Metastatic tumors of the appendix are rare. Endometrial cancer tends to metastasize by directly invading neighboring structures; the lung, liver, bones, and brain are common sites of distant metastasis. Herein, we present a case of a solitary endometrial metastatic tumor in the appendiceal mucosa without serosal involvement that mimicked a primary adenocarcinoma of the appendix. The patient who had undergone a radical hysterectomy for an endometrioid adenocarcinoma 3 years earlier presented to the hospital with a history of persistent right-lower abdominal pain. Physical examination showed tension of the abdominal muscles, tenderness, and rebounding pain on the McBurney's point. Open appendectomy for suspected appendicitis revealed a perforation of the distal appendiceal tip. Opening of the surgical specimen showed a mass that was located in the mucosa of the appendix near the appendicular root and resembled a primary tumor of the appendix. Microscopically, the adenocarcinoma of the appendiceal mucosa showed a transitional relationship with the normal mucosa, involving the submucosa and muscle but not invading the serosa. Based on the patient's medical history and the results of immunohistochemical staining, we made a diagnosis of metastatic endometrioid adenocarcinoma. The gross anatomy and histologic features of solitary metastatic tumors can mimic those of primary tumors. A correct diagnosis should be made by combining the patient's medical history with morphologic and immunohistochemical test results.