title: Classification of tumours.
abstract: Tumours are classified according to the most differentiated cells with the exception of carcinomas where a few tumour cells show neuroendocrine differentiation. In this case these cells are regarded as redifferentiated tumour cells, and the tumour is not classified as neuroendocrine. However, it is now clear that normal neuroendocrine cells can divide, and that continuous stimulation of such cells results in tumour formation, which during time becomes increasingly malignant. To understand tumourigenesis, it is of utmost importance to recognize the cell of origin of the tumour since knowledge of the growth regulation of that cell may give information about development and thus possible prevention and prophylaxis of the tumour. It may also have implications for the treatment. The successful treatment of gastrointestinal stromal tumours by a tyrosine kinase inhibitor is an example of the importance of a correct cellular classification of a tumour. In the future tumours should not just be classified as for instance adenocarcinomas of an organ, but more precisely as a carcinoma originating from a certain cell type of that organ.
authors.affiliation: Norwegian University of Science and Technology, Department of Cancer Research and Molecular Medicine, Trondheim University Hospital, NO-7006 Trondheim, Norway. helge.waldum@ntnu.no
authors.forename: Helge L
authors.initials: HL
authors.lastname: Waldum
authors.forename: Arne K
authors.initials: AK
authors.lastname: Sandvik
authors.forename: Eiliv
authors.initials: E
authors.lastname: Brenna
authors.forename: Reidar
authors.initials: R
authors.lastname: Fossmark
authors.forename: Gunnar
authors.initials: G
authors.lastname: Qvigstad
authors.forename: Jun
authors.initials: J
authors.lastname: Soga
mesh_terms: D002454:Cell Differentiation; D006801:Humans; D009369:Neoplasms / Q000145:classification* / Q000378:metabolism; D055099:Neuroendocrine Cells / Q000166:cytology; D018358:Neuroendocrine Tumors