International classification of diseases / oncology, morphological part for typing of benign and malignant tumors. The morphology axis provides six-digit codes ranging from 8000/0 to 9989/3. The first four digits indicate the specific histological term, i.e. morphology (8000 through 9992).
In developing the previous editions and the present edition of ICD-O, a particular effort was made to use the nomenclature appearing in the World Health Organization International Histological Classification of Tumours series (WHO “Blue Books”)7. This series covers all the principal sites of cancer and includes the morphology codes of ICD-O for each neoplasm. All new histological classifications or modifications have been made by the WHO / IARC in so-called "Blue Books" by 2011 are listed on-line:
http://codes.iarc.fr/changes.php.
The fifth digit after a slash (/) is the behavior code, which indicates whether a tumor is malignant, benign, in situ, or uncertain (whether benign or malignant).
A separate, 6th, one-digit code may also be given for histologic 4-tiered grading (differentiation) or for the cell type in lymphatic neoplasia.
The fifth and the sixth digit are coded separately in value sets 1.3.6.1.4.1.19376.1.3.11.34 and 1.3.6.1.4.1.19376.1.3.11.35