During the two decades since the publication of the first edition of
Histological Typing of Bone Tumours, new methods of diagnosis, es-
pecially radiological imaging techniques (computed tomography and
magnetic resonance imaging), associated with advances in the new
cytomorphological methods including immunohistochemistry, DNA ploidy
analysis, cytogenetic chromosomal investigation, etc., have greatly
improved our diagnostic tools and treatment results. These advances are
reflected by the publication of new editions of various important
textbooks in recent years. In these publications classifica- tion
criteria differed. In contrast, the WHO classification has been
relatively unaltered, and has introduced a limited number of new
entities and subdivided others because of distinct histological features
and biological be- haviour. In general the framework and the concept of
the original classifi- cation, as it has been widely accepted, remains
essentially unchanged. The classification is based on the line of
histological differentiation, in many instances reflecting the type of
intercellular matrix material produced. This approach is justified
because it avoids theoretical his- togenetic controversies.