A Case of Oropharyngeal Carcinoma Accompanying a Presacral Malignant Epidermoid Cyst

Presacral epidermoid cysts are rare benign tumors that can undergo malignant transformation. Here, we report a case of squamous cell carcinoma (SCC) arising from a presacral epidermoid cyst that metastasized to the mesopharynx. A 66-year-old female presented with abdominal pain and fever, leading to the discovery of a 5 cm presacral epidermoid cyst. Since the tumor had invaded into the rectum and uterus, total pelvic exenteration followed by ileostomy was performed. Histopathological examination revealed poorly differentiated SCC, suggesting malignant transformation from the epithelial component of the epidermoid cyst. Four years after adjuvant radiotherapy (45Gy/18Fr), a 5 cm left cervical lymphadenopathy prompted the diagnosis of human papillomavirus (HPV)-negative mesopharyngeal carcinoma (lateral wall, T2N3b). Following neoadjuvant chemotherapy, the patient underwent tumor resection, neck dissection, and free radial forearm flap reconstruction. Histopathological analysis of the mesopharyngeal tumor and cervical lymph node revealed poorly differentiated SCC with cystic formation, resembling an epidermoid cyst, suggesting distant metastasis from the presacral malignant epidermoid cyst. Postoperative treatment included chemotherapy (FOLFOX (5-FU, leucovorin, oxaliplatin)) and radiotherapy (50Gy/25Fr). At one year and five months postoperatively, there has been no recurrence of the malignant tumor. Metastatic mesopharyngeal carcinoma originating from other organs is extremely rare. While there is no established adjuvant chemotherapy regimen for presacral malignant epidermoid cysts, we preferred FOLFOX as used in the treatment of unresectable colorectal cancer with distant metastases.