Over the years, the terminology and classification of vascular tumors of bone has been highly controversial and in literature a great variety of names has been proposed. The large variety of entities of vascular tumors of bone suggests that it should be regarded as a spectrum with on one side the overtly benign lesions and on the other side the frankly malignant lesions. In between there is the intermediate category in which numerous histomorphological diversity can be seen and for which classification is most difficult. Benign vascular lesions of bone (solitary haemangiomas) at the one end of the spectrum, are relatively common and occur most frequent as an asymptomatic incidental finding in the skull or spine, although extraspinal locations are also reported. At the other end of the spectrum, primary malignant vascular tumors of bone are rare, representing less than 1% of primary malignant bone tumors.

Angiosarcoma is the most acceptable term for high-grade malignant vascular tumors of bone, which is highly aggressive with an ominous prognosis. The classification of the intermediate category of vascular tumors of bone, in particular of so-called haemangioendotheliomas, is extremely difficult due to the lack of uniform terminology and accepted histological criteria. Many authors have proposed different classification systems, but due to small numbers of cases, their large diversity and the lack of good correlation with clinical outcome none of them have been generally accepted so far. Within this intermediate category, epithelioid hemangioendothelioma is a separate and well recognized entity with morphological features exactly similar to its soft tissue counterpart, and is often multifocal.

Epithelioid hemangioma is a recently described entity characterized by a moderately differentiated, lobulated proliferation of epithelioid endothelial cells. The lesion can be multifocal, and behaves in a benign fashion although local recurrence (8%) and spread to the lymph nodes (2%) may occur. There is considerable overlap with the entity previously described as haemangioendothelioma of bone which has variable histological patterns and no distinguishing histological features could be proposed. Moreover, the entity hemangioendothelioma of bone may not only overlap with epithelioid hemangioma of bone, but also with the rare low grade angiosarcoma of bone. Therefore, there is increasing evidence that haemangioendothelioma of bone seems to represent two different entities and the use of this term should be avoided.

Chondrosarcomas are hyaline cartilage-forming tumours which can be classified according to malignancy through histological grading. Grade I chondrosarcomas rarely metastasize whereas in grade III chondrosarcoma metastasis is observed in 71% of cases. There is, so far, no clear molecular marker allowing an objective classification of chondrosarcoma. The aim of this project was to identify such marker genes through the comparison of gene expression of chondrosarcoma and normal hyaline cartilage and through the correlation of expression profiles to histological grading.

The mRNA of 19 chondrosarcomas with different histological grades and of eight normal cartilage samples was analysed. Gene expression profiles were assessed on a customised cDNA array including 230 cartilage- and stem cell-relevant genes. Data were analysed by hierarchical clustering and significance analysis of microarrays. Results were confirmed by real-time RT-PCR.

Gene expression profiles clearly discriminated between normal and neoplastic cartilage. Between them, 73 differentially expressed genes were identified. The genes higher expressed in cartilage included several genes encoding matrix proteins. Among the genes higher expressed in chondrosarcoma, molecules involved in PTH and BMP signalling were found. Genes differentially expressed between tumours of different grade were identified. Among others, galectin 1 was significantly higher expressed in highly malignant tumours compared to grade I tumours. This correlation could be confirmed at protein level by immunohistological analysis.

The comparative analysis of normal cartilage and chondrosarcoma gene expression showed that there are important molecular differences between the matrix of normal and neoplastic cartilage. Our results furthermore confirm that genes implicated in the regulation of the growth plate were expressed in chondrosarcoma. Remarkably, we identified galectin 1 as a marker correlating to malignancy on the level of gene and protein expression. More extended studies on this functionally polyvalent molecule would be necessary to establish it as a marker for malignancy in chondrosarcoma.