Hereditary multiple exostosis in a practice of pediatric oncologist

Multiple exostosis disease is a rare genetic disorder manifesting in skeletal lesions with development of multiple progressing deformations of the bones and joints. This pathology is characterized by high risk of malignant tumors accompanying bony outgrowths, primarily, chondrosarcoma with onset at the age of 20–40 years. Development of multiple exostosis disease is mediated by pathogenic variants in the EXT1, EXT2 and EXT3 genes which are inherited through autosomal dominant type of inheritance with high penetrance. During diagnosis in children, this pathology should be differentiated from progressing ossifying fibrodysplasia, metachondromatosis, Langer–Giedion syndrome and common malignant tumors of the bones, cartilage and soft tissues. The article presents 2 clinical observations of treatment of multiple exostosis disease. In the first case, familial form of the disease with transmission of pathogenic variant in the EXT1 gene from the father and development of chondrosarcoma in both sons at the ages of 17 and 21 years is described. In the second case, previously not described pathogenic variant in the EXT1 gene identified de novo in a 12-year-old patient with Ewing sarcoma is presented. These observations demonstrate the necessity of early oncological screening in patients with multiple exostosis disease.