Laboratory examination of mature retroperitoneal teratoma is mostly negative, and some immature retroperitoneal teratoma may be accompanied by the elevated levels of alpha-fetoprotein, human chorionic gonadotropin, and carcinoembryonic antigen, which have certain guiding significance for the diagnosis and prognosis.[2,8] Most mature cystic teratomas are benign, but malignant transformation of benign teratomas into various related tumors has been reported, with malignant transformation reported in about 0.5% to 3%, especially with increasing age. Here, AFP is linked to cystic teratoma.