A carcinoembryonic antigen-secreting adenocarcinoma arising within a retrorectal tailgut cyst: clinicopathological considerations.

Retrorectal tailgut cysts (TGC) develop from postanal fetal gut remnants. They have specific radiological and histopathological features that distinguish them from dermoid cysts, enteric duplication cysts, and teratomas. We report a patient with a carcinoembryonic antigen-producing adenocarcinoma arising within a TGC who underwent resection through a combined anterior laparotomy/posterior pelvic approach. Despite complete resection and delayed but complete functional recovery, diffusely metastatic disease was encountered 6 months after resection. Diagnostic, therapeutic, histopathological, and oncological implications of this illustrative case are discussed. It seems possible to use carcinoembryonic antigen measurements for treatment planning and for assessing treatment response for this rare disease. The described outcome also suggests that TGC can develop malignant degeneration and should be resected at the time of diagnosis.