Case Report: Rare malignant teratoma in the right posterior thigh

Malignant teratomas are rare germ cell tumors characterized by undifferentiated embryonic components, exhibiting invasive and metastatic potential. While teratomas commonly arise in the gonads, such as the ovaries and testes, as well as midline locations like the sacrococcygeal region and mediastinum, the occurrence of a malignant teratoma in the femur (right femur) is exceedingly rare, with limited research available. We report the case of a 19-year-old female presented with a subcutaneous mass in the right posterior thigh for 2 months, which was later confirmed as immature teratoma (CK5/6⁺, CK8/18⁺, CK7⁺, CK20⁺, villin ⁺, S-100⁺, Syn⁺, GFAP⁺, NF⁺, Neu-N⁺, CgA⁺, CD99⁺, Dasmin^-, SMA^-) with higher expression of Ki-67. Two key like pathogenic germline variants were revealed through whole exome sequencing: BLM c.2634C>A (p. Tyr878 *) and MSH6 c.3986C>A (p. Ser1329 *). This report provides information on the clinical course of rare malignant teratoma in the right posterior thigh, including treatment strategy and prognosis.