LAUSR

.c om Bone tumors are often found to be difficult by pathologists, because they are rare, and in total, almost 60 entities are recognized with considerable morphologic overlap. Similar to the classification of soft tissue tumors, the World Health Organization 2013 recognizes different categories: benign (n 5 20), intermediate locally aggressive or rarely metastasizing (n 5 10), and malignant (n 5 28), and as such, the different bone tumor entities differ widely in treatment and outcome. In contrast to soft tissue tumors, immunohistochemistry is often of limited value, although in recent years some novel immunohistochemical markers have proven their value. On the other hand, radiologic information is imperative, as for some bone tumors it is not possible to render a definitive diagnosis without taking the exact localization in bone into account. The diagnosis of bone tumors, even more so than in soft tissue, therefore needs to be established in a multidisciplinary team. Over the past two decades, an increasing amount of genetic data has become available, educating us about the mechanisms involved in the development of bone tumors. For instance, the recent discovery of isocitrate dehydrogenase gene mutations in enchondroma, or histone