Abstract
The classification of pituitary tumors is a dynamic area that changes with advances in cell biology that provide a deeper insight and clearer understanding of cell lineages and pathogenetic mechanisms. The 2004 edition of the World Heath Organization (WHO) text "Histological typing of endocrine tumors" reflects the progress that has been achieved since the previous edition of 2000. Here we review the new information and identify areas of concern for the next effort at classification of pituitary tumors.