Presacral mucinous adenocarcinoma originating from a tailgut cyst: Diagnostic and therapeutic challenges in a rare entity.

Tailgut cysts, also known as retrorectal cystic hamartomas, are rare congenital lesions with the potential for malignant transformation into adenocarcinoma, which presents significant diagnostic and therapeutic challenges. We present the case of a 41-year-old woman with a large presacral mucinous adenocarcinoma that arose from a tailgut cyst. Due to the tumor's size and location, a complete surgical removal was not possible, resulting in an R2 resection. The patient subsequently received adjuvant chemotherapy with the CapeOX regimen, which led to a significant decrease in the size of the primary tumor from 11.5 cm to approximately 2 cm. This was followed by adjuvant radiotherapy. The patient currently has no evidence of radiological progression and remains on close follow-up. This case highlights that in situations where complete surgical excision of a malignant tailgut cyst is not feasible, adjuvant systemic chemotherapy and radiotherapy can be a highly effective treatment option for disease control.