Teratoma is a germ cell tumor, which consists of derivatives of three germ layers and has various malignant potentials – from benign mature forms to immature embryonic forms with a somatic type of malignancy. Even the mature type of teratoma is biologically unpredictable providing for an ability to grow locally with invasion. Necessity for complete removal of tumors, wherever they are located, is explained by the fact that there is a risk of a possible development of growing teratoma syndrome or transformation into malignant tumors. This article describes the clinical case of growing teratoma syndrome of mediastinal localization in a teenager with Klinefelter syndrome, also as an example of the multidisciplinary approach of pediatric oncologists, surgeons, radiotherapists and pathomorphologists in decision-making for optimal treatment. The patients' parents gave their consent to the use of their child's data, including photographs, for research purposes and in publications.

Germ cell neoplasms in the group of benign and malignant tumors heterogeneous in morphological structure, clinical features and prognosis. A special characteristic of germ cell tumors is their high sensitivity to platinum-containing chemotherapy, which allows cure of up to 80–90% patients. However 20–25% of patients with a common type have overall survival rate of less than 50%. The aim of the study is to assess the survival rate of children with extracranial germ cell tumors and to identify adverse risk factors. Methods. The study includes 116 children with extracranial germ cell tumors treated from 2013 to September 2009. Treatment consisted of tumor resection and platinum based on platinum chemotherapy. Survival rate was assessed by the Kaplan-Mayer method. Prognostic factors are determined according to IGCCCG, MaGIC, MAKEI, RODO. Results. Overall and event free survival rates were 79±5% and 76±4%, respectively. The worst overall survival had patients with extragonadal tumors, advanced stages of a disease, high initial level of AFP (≥10 000 ng/ml), non-seminoma version of state treasury bills and extra pulmonary metastases. Conclusion. Survival rate in children with extracranial germ cell tumors depends on the prognostic factors. Statistically significant predictors of the poor prognosis were extragonadal localization of a tumor and the AFP level ≥10 000 ng/ml.