Enchondromatosis is a non-hereditary disease, characterised by the presence of multiple enchondromas. While Ollier Disease is typified by multiple enchondromas, in Maffucci Syndrome they are combined with haemangioma.

Due to the rarity of these diseases, systematic studies on clinical behaviour providing information how to treat patients are lacking.

This study intends to answer the following questions: What are predictive factors for developing chondrosarcoma? When is extensive surgery necessary? How often patients die due to dedifferentiation or metastasis?

Twelve institutes in eight countries participated in this descriptive retrospective EMSOS-study. 118 Patients with Ollier Disease and 15 patients with Maffucci Syndrome were included. Unilateral localization of disease was found in 60% of Ollier patients and 40% of patients with Maffucci Syndrome.

One of the predictive factors for developing chondrosarcoma is the location of the enchondromas; the risk increases especially when enchondromas are located in the scapula (33%), humerus (18%), pelvis (26%) or femur (15%). For the phalanges, this risk is 14% in the hand and 16% in the feet. The decision whether or not to perform extensive surgery is difficult, especially in patients who suffer multiple chondrosarcomas.

Malignant transformation was found in fourty-four patients with Ollier Disease (37%) and eight patients with Maffucci Syndrome (53%). Multiple synchronous or metachronous chondrosarcomas were found in 15 patients.

Nine patients died (range 21–54 yrs). Seven of them died disease related due to pulmonary metastasis (2 humerus, 2 pelvis, 3 femur). Two patients died from glioma of the brain.

In conclusion, one important predictive factor for developing chondrosarcoma is the location of the enchondromas; interestingly, only patients with chondrosarcoma outside the small bones died of their disease. In this series, no dedifferentiation of chondrosarcoma was seen. A first design flow-chart how to approach chondrosarcoma in patients with Ollier Disease and Maffucci Syndrome is in preparation.