Reference Work Entry

Encyclopedia of Cancer

pp 3108-3112

Uncertain or Unknown Histogenesis Tumors

  • Pere HuguetAffiliated withDepartment of Pathology, Vall d’Hebron University Hospital
  • , Santiago Ramón Y CajalAffiliated withDepartment of Pathology, Vall d’Hebron University Hospital


Tumors of unknown histogenesis are those in which the normal cell counterpart has not as yet been identified. Recent advances in the molecular understanding of cancer have led to classification of these tumors in terms of differentiation, regardless of their location and the presumed cell of origin.


Tumors are classified as epithelial, mesenchymal, lymphoid or neuroectodermal depending on their cell of origin. Most tumors show the histopathological features of their normal cellular counterpart and can be classified accordingly. Currently, pathologists are attempting to classify tumors according to their patterns of gene expression and markers of differentiation. An important related discovery is the so-called cancer stem cell, which has the potential to self-renew and form additional cancer cells of a similar phenotype, and to give rise to phenotypically diverse cancer cells. These cancer cells can arise from mutational transformation of ...

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