Why was HistologyMorphologyBehavior modeled as one concept?
In ICD-O-3, themorphologycode indicates the typeofcell that has become neoplastic (histology), its biologic activity (behavior), and the tumor gradeordifferentiation. The code itself has a three-part structure:
The histology code (first four digits)
The behavior cord (the fifth digit)
And the grade of differentiation code (the sixth digit)
In hindsight, the extension could have been called simply "morphology", but the name reflects the aspects of ICD-O-3 morphology code.