We report about a 14-year-old boy who presented with an anterior mediastinal mass that was diagnosed as
malignant teratoma. Surgical resection was performed along with pre- and postoperative
chemotherapy. Although elevated
alpha-fetoprotein became negative, he experienced
pain in his right hip joint 3 months after resection. Systematic evaluation revealed multiple locations of
metastasis, and the pathological diagnosis based on bone biopsy was
malignant melanoma originating from
malignant teratoma, which rapidly progressed. He died 15 months after diagnosis of the original
malignant teratoma. Diagnosing and treating malignant transformation of
teratoma, including
malignant melanoma, is difficult because it is very rare. To our knowledge, this is the second reported case of
malignant melanoma arising from a mediastinum
malignant teratoma, with both cases having a poor prognosis. In addition to the follow-up of
tumor markers, systematic evaluation, including imaging, should be considered even after remission to monitor malignant transformation of
teratoma. We expect to establish a successful therapy and improve mortality rate after more such cases are accumulated.