Introduction: Hereditary multiple exostoses is an autosomal dominant skeletal disorder with genetic heterogeneity and an estimated prevalence of 1/50,000 in western countries. Malignant degeneration is a rare (about 2%) but classical complication in patients with hereditary multiple exostoses. At least 3 loci identified as EXT 1, EXT 2 and EXT 3 are involved in this skeletal disease.
Exegesis: The case of a 45-year old man is described with 15 years follow-up after resection of a well-differentiated chondrosarcoma (grade I), which arose from a right posterior pelvic exostosis. The observed radiological lesions remained relatively stable until now. The genetic mutation which is responsible for the disease was determined at the locus EXT 1.
Conclusion: The present case report illustrates the natural history of hereditary multiple exostoses, especially since the patient underwent a malignant degeneration which could be resected without recurrence. The results of the genetic analysis contributed to the understanding of the pathophysiology of the disease.